Pros: Excellent gameplay, stays true to the formula while adding new things to keep it fresh.
Cons: Some of the earlier levels "play themselves". A bit hard here and there.
The bottom line: Sonic Rush is the best Sonic-game in years. Plays like the classics while adding just enough new things to keep it interesting.
Sonic Rush for the Nintendo DS is a pleasant surprise; its much better than the three earlier Sonic Advance games. While still not as fun as the original Sonic-games, its very close.

If you have not played a Sonic-game before, the best description is a platformer with extreem speed. Playing as the hedgehog Sonic, you have to run and jump through several levels facing many dangers, baddies and bosses along the way.

The story is the usual fare, Eggman is after the Chaos Emeralds and Sonic has to go after him. A new character called Blaze is also introduced.
Instantly when you start playing, you realize all the classic gameplay expected from a Sonic-title is intact, even though the game is not displayed in two screens.
There are loops, gadgets, powerups and the usual assortment of baddies. Running through the lush levels is fun and the split-screen display works very well and the gap between the displays is barely noticed in the heat of the action. You will also notice a slew of new things. One of the most important is the tension gauge. When defeating enemies or performing tricks in the air, the tension gauge will charge and when it is charged you can perform impressive and useful super boosts. Sometimes you will get trapped in a small area where you will have to fight enemies head to head which is a fun complement to the usual hasty running. There are also loads of new gadgets littered around the levels, making certain it will never get dull.
Another innovation is that Sonic is rendered in 3d, and so is some parts of the levels, which creates some nice effects. Which leads to the bosses, which are all in full 3d glory. Robotnic's machines really pack a punch as you have to run around and dodge them in full 3d.
There are also special levels, which reminds of the ones from Sonic 2, where you run forward down a twisting half-pipe while trying to grab as many rings as possible.
All together, Sonic Rush is pretty much perfect on the gameplay side. There is only one bad thing, which most of the newer Sonic-games share, and that is the feeling that many of the first levels "play themselves". There are big areas of the first levels where you won't have to do anything more than keeping the forward-button pressed. This isn't a big problem though, and as the levels get harder its no longer a problem.

Graphically, Sonic Rush is wonderful! Beautiful 2d-backgrounds combined with some nifty 3d-effects creates a perfect combination. Sonics animations are nice and there is a great deal of detail in the graphic. And to top it off, the boss-battles are, as mentioned, very neat.
Music and sound-effects are of high quality and follows the classic Sonic style. While nothing you will find yourself humming to after the game is off, the music suits the game perfectly and sounds nice.

Sonic Rush also has a multiplayer-mode, where you can challenge a friend in a race through the zones. You can pick up certain power-ups which is not in the singleplayer game, such as "confusion" which puts you opponent out of control for a short while. The multiplayer mode is fun and can be played either in multi-card mode or single-card mode. So you can play against a friend even if only you have the game. A very wellcome feature! You can also send a demo of the single-player game to your friends, so they can try it.