Subterrain

Executive Summary: This is, easily, one of the most underrated indie titles, EVER, on steam.
Detailed review:
First, if there is anything negative to say about this game it's two things:
1) The beginning of the game lulls you into a false sense of security and control
2) The final boss isn't really correctly telegraphed so you can't prepare for it and have to waste some time going back and preparing.
So what is this game? Generally, I divide survival games into three main categories:
1) Puzzle Survival
These are like Resident Evil where the emphasis is placed on individual survival via solving puzzles and fighting enemies. It rarely has elements of gathering, aside from ammo, and individual self-care (like eating).
2) Resource Survival
These are like 7 days to die, Minecraft, Don't Starve where the emphasis is placed on individual survival via self-care (eating, drinking, etc...) and scavenging. Scavenging nets you resources and/or blueprints that can be used to upgrade your defenses and base. These rarely emphasize puzzle solving to the degree #1 does, preferring to concentrate on the individual vs. the elements type of play
3) Logistics Survival
These are like Factorio, Mindustry, Satisfactory where the emphasis is placed less on individual survival vis-a-vie individual actions and more on logistics. Resource gathering is present, but is mainly used to drive the development of a facility. Puzzles are there, but they're puzzles of efficiency and optimization and not specific game implemented ones.
Subterrain is a weird mix of 1 and 2 with the main emphasis on 2. There ARE puzzles, but these are more like "read this log entry and look at what is highlighted to determine where to go to get the new tech up". 
Thus, there is a LOT of gathering and, in this vein, it is more similar to the 7 days to die type than anything else. However...it is ruthlessly unforgiving. In most survival games - with the possible exception of #1 - there is a point you reach where you recognize that you are, for all intents and purposes, going to win. In Factorio, it's having a factory that is basically unbreachable and producing plenty of excess, and, since you have done enough, you can now explore and not have to deal with the pressure of immediate survival.
I NEVER felt like that in this game, and that actually made it an ENJOYABLE experience.
But...
If you aren't prepared, especially at the later dates in the game, it will turn into a grind that will have any Gen Z fuck playing it crying to their parents and alleging the game is not respecting their lived experience at having always received accolades for merely booting up a game.
And this is what I mean by it being a weird mix of 1 and 2. In 7 days to die, there is really only pressure at the 7th day or at night, and rarely, if ever, do the zombies tech up beyond your ability to defend (or run) effectively, even at the base weapon tier. Here, that can happen, and it can lead to a few hours of frantic and painful gameplay. This can be avoided if you remain consistent in exploration and production, but it is a larger threat than normal; and, again, makes for fun gameplay in avoiding it.
TL:DR - the game is criminally underrated but it CAN be difficult if not prepared. If you want an easy walk in the park, look for something else. Otherwise, pick it up, you'll get your money's worth.
And, as always, comments open because I'm not a bitch

To the developers:
You've made a very good game, but it takes far, far too long to complete. It took over 50 hours of the 62 hour playtime to finish on normal, far too long given the limited variation in gameplay. If you ever make an enhanced sequel, please consider adding options for different gameplay lengths (i.e. a regular version which takes half as much time to play, along with an extended version).
More variation would be nice across the board. More enemy types, mission types, NPCs, weapons and environment types would all improve a sequel.
To potential buyers:
You'll probably like it and have fun, but you may not finish it. The gameplay is solid, focusing on a loop of explore / loot / fight -> return to base / recycle loot / get upgrades. There is some depth in the upgrade system, which involves sourcing chips to manufacture and research better versions of weapons / equipment / armour.
The survival mechanics include injuries, food, water, oxygen, heat and contamination. There's reactor you have to maintain and defend occasionally, and an infection mechanic. As infection in the different districts increases, more and more difficult enemies appear, but you can slow it down by killing enemies and placing upgraded oxygen and thermal filters. The boss fights (especially the final one) are VERY difficult.
Presentation is decent for an indie game. The story is minimal, but there are a number of quite funny logs to be found - these comic parts stand out much more than the main story, which has been done a thousand times already.

While I would recommend it to people into this style of game, I do have to say that the game is rough around the edges. It shouldn't come as a surprise being an indie-game title. I'm not saying the developers of Pixellore are bad, far from it after playing through their first published work on Steam, but don't come in expecting it to be 'perfectly polished'. Their tech support is very responsive and friendly if and when a bug come up! (even 4 years after release)
That said, let's get into it!
The gameplay loop is pretty solid. Even when behind on the crafting and tech advancements, it doesn't unduly cripple progress; which can easily happen in games of its type. It reminds of the Decision flashgame series (yes, back in the day), by FlyAnvil. What this game does differently is that it plays as tense sci-fi dungeon-crawl. The darkness and lighting effects are done well as your character relies on a mere flashlight, and sometimes muzzle and grenade flashes, to see what's going on in his field of view. Even after you get the room lights back on, you still can't take it easy, since you have a slightly less than 90 degree visual arc to work with. So keep that head on a swivel! The combat system is different than Decision, being more geared for grittier close encounters and tactical maneuvering.
Added on top of that is the survival aspect where, you have to not only worry about food and water, but most importantly infection, a few key debilitating status effects, and healing damage you will inevitability get. At the start you cannot instantly (or near instantly) heal or recover from bad status effects, which plays into the survival feel pretty well. Some survival mechanic quirks, like in-game needing restroom breaks is interesting, but thankfully doesn't seem overbearing. That aside, the typical worries of healing from damage, recovering from the occasional status effects, and managing your held resources as you loot for more seems to be executed well.
While the crafting and research mechanics is fully formed and every functional, a good part of it is for plot, ubiquitous gear progression, and much needed item restocking; for better or worse. There isn't much in the line of advanced features, crafting combos, or hidden secrets to research for building something especially exciting. It could be argued that it keeps things from being bogged down; making the process straight forward so you can get back to exploring and clearing floors. That said, crafting and researching is still enjoyable, and getting end-game gear is satisfying; but unfortunately some gear just doesn't meet expectations.
As for the rough edges, there are a few that could turn some people off if not prepared. A main one is how easy it is for a player to miss important info on their first play though, either towards progressing or towards using some features properly. While it is clear that the developers have put in a lot of work to make sure relevant info stands out, and does work well for almost all cases, some details can still slip by. Another could be the inventory system and inventory space. I believe much of that is intentional. You aren't Doom Guy, or Freeman, carrying hundreds of pounds of gear like it was nothing. That said, the general feel of the interface can feel a bit off, and the inventory management could use a couple more quality of life features (on top of the ones that are thankfully in there already). The feel of the game could be off as well, and if that's the case, do check the game settings and features. UI size, sound, camera drift, etc might not be to your liking on default settings (don't be afraid to change them!), Lastly, the combat mechanics could take some getting used to. You can leap away to dodge, plus you have an energy shield to block some damage; and while very useful, it took me awhile to get the hang of dodging on mouse and keyboard (but for others it might not). Also, being swarmed by attacks is liable to stun-locking you (sometimes to death), and there are no invulnerable frames (i-frames). Just saying! Doing stupid 'heroic' stuff is likely to get you killed. (which is likely the point)
That said, the game is pretty enjoyable, once you get the feel for it. It does turn into a repetitive grind at times (especially once you've seen all the enemy type), but that's to be expected. To my surprise when at the very end, even with the maxed out gear I got, I still had a run for my money. There is a story there, with interesting background details (and item descriptions), but you can take it or leave it however you wish; and just enough the survival dungeon-crawl.

I have owned this game for some time and I love going back and replaying it over and over. It's such a polished indie game.
You play as a scientist in prison for murder on a big scary dark base on the surface of Mars. Only after an alien mutant zombie apocalypse breaks out do you find your escape from your cell, and you now have to trudge through hordes of zombies to find a way off this red evil marble of hell in space.
You must scavenge clean foods and fluids (not just water; beer reduces dehydration levels by 40%) to keep yourself nourished. When you've had your fill, you need to regularly seek out restrooms to relieve yourself. You must also sleep regularly or else your max stamina levels can fall dramatically low and you may eventually die. Oftentimes I've found myself exploring for too long a period and I'm not able to get to home base, so I'll need to sleep on an infected floor just to keep my strength up.
You can also fall ill to conditions like bones breaking, bleeding out, or infection, in which case you need to make sure you always have bandages and fancy futuristic casts that mend your bones over several hours.
You also need to keep your equipment up to snuff. Life support has failed on this not-so-life-supporting planet, which means you get oxygen and temperature regulators for your suit. You need to make sure your personal battery packs, thermal and oxygen regulators are fully charged as you venture to nearby stations to scavenge, but you also need to be upgrading them. You can research and manufacture new weapons, equipment, bandages, and even come up with new upgraded life support modules you can use to get the nearby stations up and running, and even to suppress the infection rate of the bases local habitats.
You gotta do all this while also maintaining a central power plant. Over time, as certain facilities are powered on for light (and life support as you repair those modules), the reactor cores degrade and lose their capacity to put out energy. You can research and produce newer better cores, but you also have to make sure you can protect them with the latest of turret technology. If the overall infection level of the base because high enough, waves of enemies will start warming in from the hallways adjacent to the reactor.
This was honestly such a damn fun game, and I have not encountered a single bug. The game is beautiful, the ambiance is dark and creepy and it keeps you on your toes, but it doesn't stress you out to the point you have to turn it off for a bit and do something happy.
I really cannot wait for Subterrain II.

I would recommend it ... up until the final bosses.
The entire game 'trains' you to be cautious opening doors ... that there is a good chance you'll get overrun if you don't backpedal quickly ... but the spaces you fight in are generally narrow (or you can easily retreat so as to funnel your enemies). The crafting and other survival elements are quite well done ... but then there's the final bosses, which made me rage quit in the end ... partially because it's broken/bugged partially because the game has, at no point, 'trained' you for that moment.
First off, the bug. I stop shooting. Literally pressing the LMB does nothing. I can be shooting full auto with an SMG and then ... whoops, you're done. No more shooting for you. Try to change weapons? No animation to change weapons (although you do get the audio). Try to use other abilities? Nope. Just Exit and Reload. Again. And again. And again. And again. I just gave up after an hour and a half where maybe 2/3rds of them was because of this bug.
But then there's the bosses themselves. The first one is pretty benign once you keep your distance, he does a lot of charging WAY more than ANY other mob in the game (they're all slow, ponderous zombies, this guy is like greased lightning). Then there's the final boss ... not only does she have multiple different kinds of ranged attacks, is just as fast as the other boss, summons minions, and she has a shield that regenerates and podiums around the map that heal her. Not that it's obvious that that's what they do.
No other mob in the game heals like that. No other mob in the game has a scattershot like that. Virtually no other environment is as wide open as that. I get that you don't want the end boss to just be a souped up version of another mob, but you can have hints along the way ... podiums in other parts of the game that heal nearby zombies ... other zombies that fire off blasts similar to hers (explosive or bullet hell) ... so that we get the idea, the theme, that she's an amalgam of all these others.
I went from a walk in the park to a sudden brick wall when I hit these bosses. These were not properly vetted or tested IMO nor were they properly included in the stream of the narrative, of one ability building on another, of one environment being similar to another.

Just enough of what should be just enough to avoid annoyance (crafting, survival aspects), plenty of what should be always plenty (atmosphere, tension, feeling of progression). Simply put, it's brutally absorbing game.

Very atmospheric, the difficulty will keep you on your toes (or make you save often), uncovering the story will make you thrilled. Resource management is unforgiving but well balanced. Although some parts might turn into a bit of a grind, it's never too much of a grind.