Solid game! The concept is nice and zany, and as other comments have posted, everything is quite tight. I played it a few times and ended up getting to around wave 8.
It doesn't feel super original, but the instadeath on touching lava keeps gameplay interesting. I'm used to bullethell games having a bit more leeway on my own movement so I can focus on the things I'm shooting at, so this is challenging.
The different types of guns are fun; not sure if this is a bug, but sometimes when I have the machine gun it seems like it prevents me from turning for a couple seconds, which causes enemies to spawn faster than I keep up. Otherwise, again, solid!
More enemy types would be fun, as has already been mentioned. Also, random note: I especially like the "Get Psyched!!" font. Not sure why, it just pleases me.