Understand

Half of the game is figuring out the rules of the puzzles by reverse engineering and trial/errors. Other half is executing these rules on harder levels. Just the idea itself deserves a praise. I was having a blast for the first 4 5 hours then game started to show it's flaws. Puzzles started to lose it's reverse engineering part and rely on trial and errors which becomes tedious and boring really fast. This could have been easily avoided if later episodes had more hint levels that help you eliminate incorrect rules. But instead on later episodes the first couple of levels which are usually there to help you figure out rules started to have more red herrings than actual hints.
Also game could use a drawing feature. Many times after you figure out the rules you quickly realize on the final level of the episode puzzle requires you the execute this insane idea. Without being able to draw more than a single line at a time turns this whole process into a nightmare. This problem becomes more apparent on Chapter 4 and forward. At this point I started using a software that lets me draw on my monitor and from almost quitting the game on Cp4 I started to have fun again.
7/10

I'm about halfway through this game, and while I enjoy it a lot, I've run into a few issues where I follow the game's rules exactly, but my unique answer is not recognized by the game. Either because I didn't solve it the way the creator did, or because there was some coding error, three times in World 4 alone did I complete puzzles according to the three or four rules laid out only to look up the answer and see it was slightly different but otherwise in line with what I had input.
I still really like this game; it's exactly the kind of mind-bending teaser that I wanted after finishing Tametsi earlier this year. And, I've learned that if I can't solve a puzzle that it might not actually be me not solving it - which is kind of damning for a puzzle game about figuring out the rules. I'm not feeling bad if I look up the answer to a puzzle or check the rules if I'm pretty sure I've figured it out, because I can't trust that I'm actually wrong.

this game would be good if 4-9 didnt exist (i still recommend)

In short, Understand is all about understanding a set amount of rules that each level draws from in order to solve each level. You are given no hints about what the rules may be; only examples that you have to derive each of the rules in the set from.
When first beginning this game, you have to understand that this is going to be a difficult puzzle game, which it truly turns out to be. Sure, the first world isn't too difficult, but as you progress along in the worlds, each rule in each set of levels slowly becomes more and more obtuse, and some levels have special rules that don't appear in other levels.
The good thing about this game is that they confine each rule set for each level set under a theme for the entire world, which should easily be able to be deduced as you go along with solving the levels. That being said, there is a singular level in each world (usually unlocked after beating the 10th level of each world that ends in a ?. These levels in particular usually have some sort of gimmick thrown into them that can make for some extremely frustrating levels.
You should keep Paint handy as you will more than likely have to use it in order to solve some of the levels in the later worlds. You should also keep Notepad or another word processing program handy in order to keep your current hypotheses about what the rules are for each level set.
With all of this being said, the level design is very well done, however, it feels as though some of the levels have arbitrarily set rules which can easily make a player frustrated and/or stuck on said level. With progression locked behind reaching certain levels in each world, getting stuck on earlier levels in the world has the potential of locking the rest of the game behind levels that you could possibly get stuck on. All I need to say is that there will be levels that you will inevitably be stuck on in this game, and you should feel no shame if you have to get a hint for some levels from one of the many guides available for this game.
I personally turned off all audio for this game besides sound effects because I found that this is one of those cerebral games that requires a ton of focus, and having the music on can easily distract you when solving the puzzles.
Overall, this game is very well done with a few obtuse exceptions that could lead to a player getting extremely frustrated. If you are going to try to get all of the achievements in this game, and you don't plan on using any of the guides available to you, you should expect this game to take up to 30 hours to 100%, or if you get some hints from any of the guides available, maybe 15-20 hours to 100%. It is a somewhat easy recommendation for those puzzle players that like somewhat obtuse puzzles without any hints provided. If you like games such as Tametsi, FEZ, or any of the Hexcell series of games, you will also like this game and the price point is very reasonable.

"When you're thinking about something that you don't understand, you have a terrible, uncomfortable feeling called confusion. It's a very difficult and unhappy business. And so most of the time you're rather unhappy, actually, with this confusion. You can't penetrate this thing. Now, the confusion is because we're all some kind of apes that are kind of stupid working against this, trying to figure out how to put the two sticks together to reach the banana and we can't quite make it. And I get this feeling all the time that I'm an ape trying to put two sticks together, so I always feel stupid. Once in a while, though, the sticks go together on me and I reach the banana." - Richard Feynman

this game sucks