I will deliberately take a contrary position just for the sake of writing incredibly long arguments
I bit during the Black Friday sale. Mean old Mister Creaphis has a few criticisms. I'll start with things that you could actually change with easy tweaks.
Monster sub-types aren't visually distinct. Slight size and head colour differences aren't obvious at a distance. Instead of colouring your main grunts blue, blue and slightly purplish, make them green, blue and red. Important projectile differences aren't distinct either - make a completely new model and sound cue for the purple dude's homing bolt. A constant "sizzle" or something like that lets the player know he has to keep an eye on that thing.
Your basic grunts don't telegraph their attacks properly - they shoot their bolt while they're still raising their gun. Playing against these guys would be more fun if their attack was delayed to the end of the firing animation, but then made more damaging. Reacting to a threatening attack and then dodging it is interesting. Constantly circle-strafing just in case you get caught off guard by an enemy's pea shooter is not.
I'm not sure what gameplay purpose the "sentries" serve. Fighting them has a lot in common with playing as a sniper in a modern shooter. You're clicking on a small target at a distance that wanders into your crosshairs in a predictable pattern. It's just a robot instead of a terrorist's head. This is the opposite of the Doom-like, Contra-like gameplay that I understand is your objective. I recommend keeping the sinusoidal bobbing but making these things rush at the player one at a time to make a melee attack, like Castlevania's Medusa Heads.
The player's movement speed is actually too high for what you're trying to do. This makes the platforming too "slippery" because the window of time between starting to move off a platform and falling off the side of it is very slim, making jumping difficult and unforgiving. The monsters also aren't nearly threatening enough to justify giving the player this agility. I feel like I'm Superman, soaring around, murdering forest creatures. Once in a while I get nailed by an acorn but it never matters.
I've been playing on the middle difficulty level, which is the difficulty you should design for players who are already experienced with shooters in general but don't yet have whatever advanced skills your game might need. In the levels I've played so far I was never in any remote danger of dying in combat - only a few platforming mistakes did me in. I showed this to a friend yesterday and found that I'm able to play and converse at the same time without slowing down at either task. It's mindless and unchallenging.
This last point is more of an academic one, since I realize it's far too late to rebuild every map to suit this, but your game needs hitscanners. I know, it seems like forcing the player to take cover now and then would make the game less fast-paced, or hectic, or whatever the desired adjective is, but the truth is counter intuitive. When you put a dangerous hitscan enemy on one side of a large arena, the safely maneuverable area is restricted to whatever cover the player can find. Then, if you throw some projectile and melee enemies at the player at the same time, he must dodge and maneuver in a much tighter "effective arena." This tension is necessary to make projectile and melee enemies interesting. Hitscanner enemies can also move, meaning that this effective arena changes size and shape and the player must be reactive to these changes. Arenas become dynamic even when they're just made of stationary map features. You end up with a lot more gameplay for the same developmental effort.
As far as the game's packaging goes, I like the in-game art design and the engine is solid. I'm not convinced that the dialogue between missions adds any value. Note that I'll eagerly sit through fifty hours of voice acting in a Mass Effect game, while I couldn't bring myself to read Wrack's inter-mission quips. I understand some people like groaners, but it's a very narrow aesthetic that most people don't enjoy, and putting writing like that in a project like this is risky.
I am rooting for you Carn. I wish you success. This is how I show it: with the tender sweetness of a seasick crocodile.