Not the most realistic, but definitely the most fun soccer game available!
I played Fifa 06 a ton on the regular xbox, as well as winning eleven 9, Fifa 07 for xbox 360 a little (hated it), and Pro Evolution Winning Eleven 2007 a little on 360, so those are the games that I'm going to be comparing Fifa 08 to.
Graphics: Ffia 08 is definitely teh best looking soccer game to date, as should be expected. Player models are better than ever, both close up and during normal gameplay.
Sound: The announcers are the best they've ever been. They say the names of the players as they receive the ball, which is pretty cool. The crowd and field noise is excellent as always as well.
Gameplay: This is definitely the most important aspect of the game, and Fifa 08 has truly excellent gameplay. It's hard to explain, but 08 feels and plays the way I want a soccer game to play. The trick system (hold left trigger and move right thumbstick) is really fun to play with, and it can help you juke out the last defender to get that game winning goal. Honestly, it's hard to say much more about the gameplay without going into tiny details, just know that this game seriously plays great.
All-in-all, this is a really sweet playing soccer game that is simply a ton of fun. I don't think that the learning curve is bad at all, but it could definitely take some getting used to if you haven't played a lot of soccer games before. This is the soccer game to buy for xbox 360, all the other 360 soccer games hardly compare.