Jumping past spikes from the side or touching a few pixels is an instant kill. I jumped twice without moving left or right or shooting, and the second time was killed.

I like the game’s sense of progression, especially at Level 4, which feels properly like an endgame. By comparison Lvl 1 is boring and Lvl 2 is lucky. I think that progression would be stronger if later levels gave you some insulation from death instead of just a bigger gun.