The music, sound effects, graphics, and gameplay kept me so engaged I came back to finish this game. ^^ It was fun!
For a serious critique, there's nothing I can add more than everyone else who has commented.
But, uh, one time I couldn't quite get a life in the 3rd level, so I started mashing the directional buttons and jump, and I, uh, started flying! I'm not sure if that's a glitch at 0 velocity or some invisible platforms you specifically put in there to reset jumps, but, uh, well. .//. I must admit that was an enjoyable twist to an already enjoyable game!