Damn it. I've always loved Fancy Pants and I'm really not sure what I can say that hasn't been said already. The physics are impeccable. The animation is impeccable. This game is eye candy and finger candy - the controls are incredibly responsive and are polished to the point that they reflect more light than the moon. Grabbing, sliding, rolling - this game has all of it, and for every little thing is a seamless animation.
Now, that aside, there are a ton of problems with level design. It's not so much that there's anything wrong with the levels themselves, but more that the environment isn't challenging. You can waste a lot of time exploring, and the boss can prove to be a challenge due to only being able to take three hits, but the game doesn't really incorporate the fast-paced potential of this game into actual gameplay. You can look in the trophy room to see your fastest completion and that's literally it. The terrain is fairly boring if you're not interested in exploration and in the end it feels like one really long first level to a game. I'm still giving this full marks mainly because of what I stated in the first paragraph, but I think the principle still stands.
For everything it has going for it, Fancy Pants is ultimately brought down by its own simplicity. The bonus levels and snail shell objectives give this game quite a lot of replay value, but there isn't really much to challenge the player in a more high-octane environment, and that's really the direction a game like this should be going in. I would like to see time trials, and perhaps some puzzle elements or powerups to make the game a little bit more challenging. The hop-and-bop combat mechanics are fine, but the enemies are redundant. This definitely needs more.