If you're an old-school fan, you'd be doing yourself a favor by getting Sonic Rush.
Very fast
Graphics look nice
Strange, but catchy, soundtrack
Challenging level designs
The Bad:
Bad enemy placement and numerous bottomless pits result in cheap deaths
Blaze's levels are no different than Sonic's
Sonic Rush is a 2D platformer that brings us plenty of new additions such as the "rush" move and the trick system. We also get a new character known as Blaze the Cat. She's probably the first worthy female in the Sonic universe due to the fact that she's not annoying and slutty like Amy and Rouge are.
Story
Well... it's a Sonic game. If you want a Sonic game with a "plot" go play the Sonic Adventure titles or Sonic '06 (if you're desperate).
Graphics
Sonic Rush is a fairly good-looking game. The 3D graphics and animations are a bit rough around the edges, but the 2D graphics and animations look pretty dang good and are very pleasing to the eye.
Sound
Sonic Rush has a very upbeat soundtrack, and it's both creepy and catchy at the same time. Random noises and catchy beats are combined together in the game's songs and that makes them very strange, but also very likable. Some of the songs get so strange, however, that it makes you wonder if any of the songs were written on ecstasy. That isn't always necessarily a bad thing though.
Gameplay
Sonic Rush is very fast, very fun, and very challenging. The levels are designed very well, but you can expect to run into awkward stumbles along the way. The bottomless pits are often too plentiful, and the enemies are often place right in the middle of where you're trying to run. These factors can result in cheap deaths, and they can also make you a bit paranoid to run fast because of the random bottomless pits and enemies you might run into. The difficulty of this game is pretty well-balanced for the most part, but it's going to take a bit of memorization from time-to-time so you don't make the same mistake twice. Overall, however, Sonic Rush is a very fun game, and the levels are well designed (even if they require some memorization).
Speed
Like I already said, Sonic Rush is very fast. Old-school fans will appreciate its insane sense of speed, and the addition of the "rush" ability makes you go even faster, which helps you plow through the poorly-placed enemies without any troubles. Few Sonic games are as fast as Sonic Rush.
Overall
If you're an old-school Sonic fan (AKA a TRUE one...), you'd be doing yourself a favor by getting this game. It has its moments of frustration from time-to-time, but it's still a fast and fun experience.
Story - 7.0
Graphics - 8.5
Sound - 8.5
Gameplay - 9.0
Speed - 10
Bottom line: if you're tired of crappy Sonic games and want to play one that's actually good, then get Sonic Rush.