This is a pretty interesting game- and definitely a great one, as your first project!
First of all, I would like to say that shooting enemies in this game is really fun- even though it's sometimes hard to directly hit enemies with the spread of the shots, the sound effects and the splatter all contribute to a nice experience. I also liked the size of the bullets as well- since most people try to use tiny bullets in their first game (for realistic-ness and accuracy) and fail.
In addition to that, the maps are usually fun, unless there's blue goop cornering you, and then you're usually done for.
There was one big problem that annoyed me a lot, though, and it is enemies spawning on top of me. I was standing near the edge of the map, and died 3 times in a row without any solid reason.
Maybe spawning the enemies at a certain random distance from the player, or having a hole or a gate that indicate that enemies would spawn out of them can solve that- and there's probably a ton of other ways to fix that, so I don't think that should be much of a problem to fix.
The first time I faced the one-eyed blue goo monster, I was killed shortly after- it takes several deaths to get adjusted to the blue monster, and the ability to run away from it depends on the amount of red monsters on the map and their spread.
There was some time when I was cornered by a mob of red monsters on one side, and a blue monster on the other- it was a pretty hopeless situation, that I guess could've been prevented by me avoiding the blue monster or running away from it without shooting it- but not always it's possible to run away from the blue monster while avoiding the red ones and still feel skilled, or not die.
However- I though that the green monsters + red monsters combination was really clever- the green monsters were stuck every now and then, but in the end, they were a pretty fun challenge. In addition to that, I liked how the eyes of the red monsters become a bit bigger when they notice you, and the fact that blue monster blood makes red monsters slower. The synergy between the monsters is definitely a strong part of this game, and it would be interesting to see similar stuff in other games- since this is more than enemies complimenting each other, but rather enemies affecting each other in interesting ways.
Technically, a similar thing would be an enemy cleric healing his fellow enemies, or an enemy mage buffing other enemies, but besides that I can't think of many examples of enemies affecting other enemies, in ways different than adding more firepower to their side or acting as meat shields. It would definitely be interesting to see something similar in a rogue-like (or rogue-lite, however you may call them), I think.
Also, the flashlight level is really interesting. I'd love to see a blue monster in a dark environment with a few red enemies, I think that would make for something interesting- but that's just an untested hypothesis, hehe