Most likely the shortest GBA game you'll ever play. Other letdowns will disapoint Sonic fans greatly too.
The worst addition to Sonic Advance is that Amy (a pink little hedge hog with a crush on Sonic) is in the game. I don't know who's bright idea it was to add a slow, clunky character that can barely make through levels in the game, but they really need to look at what they did.
It looks like they tried to make the game seem like it lasts longer by adding a Chao garden, but this is hardly as fun as the Chao garden in Sonic Adventure 1 and 2; all you really do in this Chao garden is feed them and play 2 really annoying mini games over and over to help you get more fruit for your Chao. If you beat the game, you'll be given the chance to fight robotnick using Super Sonic, just like the old games, accept with way better graphics.
Actually, the only saving grace of this game is the smooth hip graphics that add a pretty nice and bright look to everything. Otherwise, I'm appalled over the amount of people that think this disgrace is a plausible addition to the Sonic library.
A very short game, with a broken Sonic formula that will have you barely sprinting around and only a couple ways to beat each level, compared to the many different ways the old games had. If you're a hard-core gamer, this just won't float your boat for too long.