(For reference, I played the Windows version, not the web build)
Right off the bat, what stuck out to me was the main character design, which was quite unique, as well as the tutorial signs on the walls, which are a nice way to tell the player that they can use those keys to do things.
The pixel art has a cool style to it and the fog of war makes exploring a mystery that you need to be careful of.
One of the things that stuck out to me on by far was the ambientation. Knowing the context of the game, the game has a hint of tragedy for me. Especially considering that you and all of the other creatures are products of experimentation. The dog with wheels is certainly an example (really cool enemy designs too, by the way).
A couple of touches I also appreciate is the fact that shots have a very bright light attached to them, so you don't miss them in the map, as well as the fact that enemy shots get deleted when their source enemy is defeated.
I noticed that the flamethrower particles and the damage numbers have very similar colors, so it can be hard to tell one from the other when attacking with the flamethrower. Also, the enemy with red hair that shoots you can sometimes shoot you while they're walking. Their shooting animation doesn't play when that happens; they only keep walking as their shot spawns, so it can get you off guard, since there's no anticipation.
I also noticed that you can get the same weapon spawning in both chests of the same floor, which can be a bit rough if you don't like the weapon (which happened to me). I'm not sure if this is entirely intentional, so I'm pointing it out here.
I definitely felt a bit of a difficulty spike on the last floor, since it introduces new enemies that are quite tough (the slime and the spider cyborg thing). It more enemies, some which can feel tanky, like the big security guards and the slimes. I do appreciate that they're slower though, so it lessens the chance of them pushing you into rooms and drawing the attention of more enemies.
The music variations were welcomed. They were all bangers. Very good choices! The sound effects also felt fitting.
One thing I did miss on the game was having some sort of map or minimap. It can be a bit easy to get lost on the levels, and I think the game could really benefit from having a map function, especially so you can keep proper track of what areas you haven't explored yet.
With all of that being said, I enjoyed my time with this game. The controls feel intuitive and fun to use, some of the weapons were a lot of fun to me (like the long laser gun), I like some of the humor the game has, and the enemy variations were unexpected and quite impressive. Very well done!