DUDE! This game was such a blast. This feels like with some more content it could become one of the classics of arena based shooters like this.
The shooting felt great, from the blast effects, the robot death animations (it's really hard to make shooting a robot feel satisfying in a game) and the sounds it all worked together really well.
The music, while there's only one track it worked great for this type of game.
I played until I reached level 7 (on Normal) since by then I'd reached max level.
The regeneration power is a bit OP, after I got it I could choose stuff like less max hp and shields and no health drops without ever having to worry much. This might not be as much of a problem one higher difficulties of course =P
If you ever develop this or something similar into a bigger game I'd recommend focusing a lot of effort on increasing the level variety. The rooms looked fairly varied visually but gameplaywise most of them were just an open field. More room varieties with the walls and pillars would be nice. Floor hazards perhaps? Both of the spikes and mines type but also just holes that you (and enemies can be slung into by knockback. And on the same note, spikes on walls or something like that for the same reason.
Another thing when it came to the level design, while you could walk back the way you came from, it took until floor 6 until I ever ended up in a dead end and had to do that so it felt like a bit of a wasted feature... not that this is a game about exploration of course =P
Great work! This earned it's 1st place win for sure.