Damn, what an awesome game. Graphics are awesome, the art-style is just great. Difficulty feels about where it should be. It's pretty fair and strafing around dodging bullets feels pretty good.
The conflicting tone between the cheery player and the hellish world is really neat.
- Weapon/explosion sfx don't really match the impact they have visually
- Music kind of drowns sfx out, by default
- Issue where an enemy spawned basically on top of me, resulting in an unavoidable hit. Link: 
- First encounter with portals could be confusing, since orange/fire-y things damage you otherwise.
Again, awesome game.