Warframe

Get the Excalibur frame.
Spend your starter plat on frame/weapon slots
buy a shotgun with credits as soon as you can
Once you've inevitably gotten addicted to the movement and controls, pop open the Warframe wiki and look into weapon and frame crafting.
This is your life now.

I'm bored of this game. I can barely play it. A lot of the new content is more of the same. This is a common theme between veterans, as you can see from several negative reviews from people with 1k+ hours into the game.
HOWEVER...
If someone played a game for this many hours and stopped because of the lack of content, it's not due to the game being unfun. The average player will find the game quite entertaining for the most part. There's just too high of an expectation of being able to play a game 10 hours a day and not get burnt out.
It's an amazing game. By the time you are bored, you'll have spent more time in this game than you'd ever have on several "AAA" titles combined. And it's free. The monetization is absolutely fair (and extremely cheap). Seriously, if you get a 75% discount on one of the Daily Rewards (not an uncommon reward), any plat purchased will net so much value and for a long period of time.
TL:DR Try the game out. It's known as the King of F2P for a reason

It's been almost 7 years now. Being with this game for that long as a founder, you see a lot of good... and a lot of bad.
Do I recommend this game? Not for everyone, no. There's been many bad choices leading up to the current state of Warframe that has left many veteran players discontent. Hell, even I feel burnt at times. If you're looking for a game to no life everyday for the rest of your life, I'm not sure if you'll find it in Warframe in it's current state. The lack of a true endgame and the current nature of recent updates catering to new players over old has made the game wider but not deeper. For the other type of players that are more... let's just say sensitive, you'll find that the community has certain perks that may discourage a few behaviors. For one, begging for free items is heavily frown upon. Similarly, if you ask for help on mundane and simply task that anyone can do (that includes using Google), you'll find many people to not be receptive of your inquiry. The community is not so much toxic but rather passionate. The ones that truly stick it out knows that one of the best ways to enjoy Warframe is to build yourself up with your own hands. So if you're the type who likes their hand held 24/7 or be boosted/rushed to the "endgame," steer away because you won't be welcomed here.
Please also be aware that, while there is an extensive in-game market, it is by no means a pay to win model. Virtually all items that is prevalent in gameplay is farmable and the premium currency is actually tradeable between players. There is a very prominent trading community in the game and if there's something you want, someone else most likely has it. The somewhat convoluted menus and lack of proper tutorial contribute to the confusion. However, do not be discouraged once you've seen it for the first time.
In regards to update, it's quite a mixed bag. Because the developers do not have a fixed schedule, updates can either be extremely frequent or extremely sparce. And much of the content content you get can equally be as randomly enjoyable or otherwise. There is a massive array of activities you can do and it really boils down to your preference what you like or what you don't at all. It really is an effort by the devs to cater to everyone. Or atleast they try to.
You may also find that many updates come with an astonishing amount of bugs. This dissuades many players but I just want to pose a quick question, why don't you just not play the content until it's fixed? Since most activity are in essence optional, it's really up to you if you want to do it. No one is "forcing" you to play it, as I have heard many complained about before. If you feel forced to play a video game, that's more of your own priority issues, not the game. But the real caveat is, this is just how the game updates operate. Because one of the most important factors of Warframe is community and developer communication. Updates and fixes are very frequent and fast (minus holidays naturally) and the only issues that are usually left unchecked are miniscule or ones that are difficult technical wise. Other than that, it's not as much of a slough as many would like to proclaim. The devs give content to the players, players give feedback, developers start patching as soon as an hour after the content drop.
For the veteran players, do I think the game need a lot of work? Absolutely. I won't deny that current content drops have not lived up to the expectations of many but it's also mostly pointless to whine about it. If you truly no longer enjoy the game, get off it. Go live your life, play another game, and if the day comes, come back to Warframe. But if you truly want to make a difference, get on the forums, get in game and spread the word, create some influence. Be an actual member of the community rather than a ragtag pitchfork mobs. In the end, it's just a game and you can leave and come back anytime.
I'm not trying to be a white knight nor am I trying to hide the miscontent of many players, I just find it unproductive to whine and mope about. If a game really does bring about the worst in you, don't play it, it's a pretty simple concept. If you do want it to be better, finds way to help improve it, screaming your miscontent does no one justice. Not you, not the developers, not the game. Unless of course, you think it's morally right to riot and form a lynch mob, in which case I'm sure you can find the developer's address somewhere. In all seriousness though, I understand that some pressure is needed to push the devs to steer towards the direction we the community want but we often forget that they're people too. So unless you have never made a mistake your entire life, you're not in much of a position to talk :P
Make clear your mind but keep it civil, productive, and educated. You're better than that. We all are.

Get out while you still can.

Warframe is a deeply engaging and rewarding game that just keeps expanding in scope as you get deeper into the experience, and the development team gets ever more ambitious in their expansion of this title they've clearly poured so much love into. Before I rave about how good this game is though, let me tell you about gripes people have with the premium currency inherent in any free to play model. None of these things bother me, and I'll explain why, but they might bother you, and its good to know what you're getting into.
Warframe is often pointed to as an example of the free to play model at its best, and for good reason. The game is very fair and enjoyable whether or not you choose to spend money on it. You can pay money for an in-game currency called platinum that you can use to purchase cosmetics or speed up progression. I think speeding up progression is what most people would have an issue with at face value, but honestly, I think its better to not spend any platinum doing this, even if you have money to burn. The progression is an integral and rewarding part of the experience, so skipping over it is really just robbing yourself. You'll feel a lot more proud having earned it yourself. I purchased platinum to support the developers, and I spent it all on cosmetic bobbleheads for my ship because I didn't want to mess with the experience. I think that says a lot about how good the gameplay experience and progression is.
The one platinum mechanic I think people will have the most issue with is time-gating. Crafting items in this game takes significant real-world time, which you can pay platinum to skip, but this is a terrible waste of your platinum, and you should never do it. Some items can take 24 hours or more to craft, but this is the kind of game where you are supposed to plan ahead and have many kettles on the fire at once. Get a bunch of weapon schematics and start crafting as many as you can with the resources you have. There's no limit to the number of crafting projects you can have active in the foundry at once, so go nuts! Before you know it, you'll have 6-10 items sitting finished in the foundry ready to be claimed at any one time, and you might leave them there for weeks while you're leveling up your other weapons. No need to waste inventory slots on something you don't actually want to use yet.
That brings me to the other big restriction tied to platinum. Inventory slots. In a game about collecting as much shiny space stuff as possible, placing restrictions on your inventory slots does seem a little harsh. Up until recently, it was recommended to spend your free starting platinum on these, but with the introduction of nightwave missions, they've added inventory slots as an in-game reward you can get each month, and with pretty minimal effort a lot of the time. A single play session today got me to the x2 weapon slots reward tier in Nightwave. Honestly, the average player is likely to complete enough Nightwave challenges by accident while just playing the game normally that they'll get these things. So maybe hold on to your starting platinum a little longer and see if you really need it.
The last gripe about platinum, and one that bothered me the most personally, is color palettes. There are many available in the game, but almost all of them cost platinum. Some holiday and special event ones will pop up for free from time to time, but your starting selection is quite limited, and if you care about aesthetics like me, then this will bother you. Honestly, I think this is what I would spend my starting platinum on if I restarted the game today. I would recommend buying one of the classic sets with a rainbow assortment of colors, and then probably the Grineer color palette. Grineer comes with a nice assortment of blues, oranges and greens, but more importantly, a great assortment of blacks and greys, which are perfect for giving your weapons a metallic feel, or for contrasting the bright colors on your warframe with more mechanical-looking parts. Thankfully, if you're absolutely determined to unlock all the colors and cosmetics you want without spending a dime, the game has a vibrant trading scene both in and out of game. If you find that kind of thing fun, you can make a lot of currency just from dealing in in-game goods, or selling off rare mods you got extras of.
END OF GRIPE SECTION
Now with the tedious section about money and currency models out of the way, what does it feel like to play Warframe? Well, in short, really really good. Lets start with the in-mission gameplay. Your warframes are incredibly fluid and mobile. You can jump and dash and roll and slide with ease. The more you play, the more you'll feel like a graceful acrobat, and there's plenty of depth to the movement system you'll learn as you go. For instance, one of the fastest ways to get around in a normal warframe is to slide, then press space to bullet jump (a sort of twirly jump that happens when you press space while crouching or sliding, which gives you momentum and can be used to reach high places), then, just as you're entering the bullet jump, tap the sprint/roll key to go into a midair roll. Rolls gain you a quick burst of speed, but normally slow down at the end due to friction; not if you just launched yourself into the air though. And the roll animation ends just in time for you to go back into a slide and maintain all that momentum when you come back into contact with the ground. Your warframes are also kitted out with a wide array of abilities that all have creative and satisfying ways to employ. Its refreshing to have so much freedom in a game. At high levels of play, it becomes a game about mowing down hordes of enemies as quickly and efficiently as possible, almost like the engame of action rpgs like Path of Exile and Wolcen, but as a third person shooter. Its difficult to explain just how good this game feels without you experiencing it for yourself, and its completely free, so please, do yourself a favor and give it a try.
As for the out-of-mission gameplay, it'll be a bit of a rockier start. The game has an incredible amount of depth for veterans to play around with, but this leads to a bit of a confusing experience for new players. At first you will be utterly lost and aimless. You'll have a vast universe to explore, 99% of it currently unavailable to you. Dozens of different resources with functions that are utterly obscure to you. A whole row of tabs with different types of missions to do. Terminals to interact with. Challenges to complete. You'll be lost, overwhelmed, and just ask yourself "What am I supposed to be doing. What is my goal here?". And that's one of the interesting things about Warframe. There is no real goal. At least no obvious one presented to you. Instead there are a bunch of different interconnected systems you can interact with for rewards, and what you deem valuable becomes your goal. Starting out though, you should just try to level up your equipment, unlock more of the star chart, and collect some mods for your equipment, which you can attach to it through the arsenal in your ship. Get a few weapons brewing in the foundry, and once you feel like you understand what's going on, you'll set off on your own, start setting and achieving your own goals, and start to really appreciate all those systems that were confusing and overwhelming at first.
If you ever feel lost in the game, don't be too shy to use the chat. One of the greatest assets of this game is its wonderful community, and veteran players are always more than happy to answer questions, and even help you with missions you're having trouble with. I got a lot of help when I was starting out from some really cool people, and now that I'm a veteran, I've returned the favor many times over.
In conclusion, Warframe is one of the best games I've ever played, and its more than worth the time of installing it and trying it out. Do it. NOW!

The short version:
1) It's free, except cosmetics and things, but you can trade other players for in-game currency from items you obtain in-game...so still free.
2) Devs are great and very interactive with the fandom. Is this why I buy things in the shop? Yeah, not because i'm lazy and irresponsible with money. It's definitely support. Definitely.
3) Every other game is now slow-motion to me.
4) CLEM.

The best Free to Play game ever created, with the best in game currency economy. Don't want to pay money for platinum(in-game currency)? You can earn it from trading. You can spend your money on prime packs and platinum, rush everything and have things available to you right away if you choose, but its not mandatory, ever. Zero Pay 2 Win mechanics.
The amount of content, story, planets/locations, weapons, warframes, and pets is more than 3 Triple A games worth of content, and more is coming as well as constant in game events on rotation.
Might be a bit overwhelming for new players at first, but if you push through and unlock each planet, you'll soon understand what you want to do.