Fun!
Gavin rocks! I likes him.
The cartoony characters are great. Gavin is a great character, just wanting to have fun, and playing the game his way.
Anyway, the only constructive critisms I have are:
1. Gavin doesn't see to roll right. He starts his jump orientated up and down, and then starts to roll for no apparent reason. Maybe I'm nitpicking, but it's distracting to me. Why did he start rolling? If he's going to roll, he should leave the ground with a slight roll, then tuck his limbs so he would roll faster in the middle of the jump. Anyway, please forgive my nitpicking.
2. Some of the background graphics aren't tiled together perfectly. There's some overlap or breaks. More nitpicking from me.
3. The only challenge is the boss. It's fustrating to play the whole game over just to replay the boss. If the boss kills you, I suggest starting the player over at the boss.
Thanks for the game!