Sonic returns to his two-dimensional roots, but fails to impress.
Sonic Advance was one of the first games in the series to appear on Nintendo hardware. Sega enlisted DIMPS, a game development company formed primarily of ex-SNK members. This trait shines through immediately in the form of visuals: Sonic & Co. seem to stylistically fit in with the Metal Slug series, and they animate very smoothly. Visuals over-all are very nice; a clean, hand-drawn style permeates the entire game - definitely a big step up over the usual quick-and-dirty Pre-rendered sprites most Gameboy Advance developers go for. Sound is as it should be - rings sound like rings, for example. Musically, the game has a slightly laid-back tone to it, with a little bit of jazz thrown in for good measure. It won't stick in your head as well as, say, the tune from Green Hill Zone, but it's not exactly terrible by any measure, either.
In terms of gameplay, Sonic Advance picks up directly where the Genesis titles left off, practically without missing a beat. If you were a fan of Sonic the Hedgehog 3, this game will be immediately familiar to you: Sonic controls exactly as he did in that game. In addition to Sonic, you can play as Tails, Knuckles, and, for the first time in the 2D realm, Sonic's would-be girlfriend, Amy Rose. Each character has distinct control advantages over others - Sonic is more suited for head-on speed, Knuckles is suited more for exploration, and Tails is somewhere in-between. Amy Rose diversifies this a little further by adding a character that seems to challenge the player a little more than usual - she is arguably the slowest of the three, and cannot spin. This makes her play completely differently from the original three characters - you have to be very careful and methodical when encountering enemies and obstacles as Amy.
However, even with Amy Rose in there to break the gameplay up, Sonic Advance feels a little too by-the-books. Despite unsuccessful attempts to merge some of the gameplay quirks from Sonic Adventure (such as grinding), Sonic Advance just doesn't innovate enough to really be interesting - and add on to the fact that level design as a whole is really uninteresting, with gameplay gimmicks being re-used for many of the levels (leading to a lot of "I already did this" gameplay) and the whole package feels ho-hum. Nothing feels particularly outstanding. Even the bonus stages, something to strive for in the original games, are boring - and kind of cheap in terms of difficulty. Even finding the entrances to these special stages (characterized by an "Uber-Spring", hidden deep within each stage) is a chore.
Difficulty-wise, the game varies. Most stages aren't particularly difficult, and shouldn't take you very long to clear. Bosses range between "really boring and tedious" and "frustratingly stupid". None of them are really amazing by any regard, and a couple are even recycled from past Sonic games.
Overall, what we're looking at here is a game that is neither outstanding or terrible. If you're starving for a Sonic game, this will quench your thirst somewhat - but generally, there are better alternatives available on the market.