I played a bit of it.
On the second stage you can get pushed inside the walls if you don't move quickly enough.
The bosses are neat but you should give them a visible health bar (unless I'm just blind). Also you should make the invincibility time match/extend past the blink effect time. I got hit a bunch of times when I thought I was still invincible.
I never considered giving the bosses a health bar, that shouldn't be hard to do though. And I thought the invincibility timer was a little off, but the effect should match the timer.
I'm glad you actually got to the second level. I gave this to one of my real life friends and he said he couldn't beat the first level...I didn't think I made it that hard.
The walls are a hard bug to eliminate, but I managed to make it easier to wiggle your way out of them.