This is superb - the Xbox answer to Gran Turismo. I was sceptical at first of it but picked it up at a good price from play and wished I had done so a lot earlier as I really enjoyed the Gran Turismo series.
It's a racing simulator so isn't to be compared with NFS as you can really fine tune your cars here for proper noticeable differences. Try racing a car with all the upgrades on standard settings then tweek the settings and marvel at the difference in the way the cars handle.
In essence all driving games are repetitive so if you find yourself getting bored very quickly with games of this nature then it probably isn't for you. There are plenty of race classes and country classes to get your teeth into with the customary endurance races (these only last 2 hours though which is good)
Online play against people who genuinely want to play the game is fantastic but there are some cowboys who just come on to knock you off the track or take your car out which can be frustrating. You can turn the collisions off to avoid this if you wish so at least you have the choice.
There are some extra cars and tracks you can download too so you can expand on the standard game (extra cars are not needed to complete the game 100% though)
This is another must have 360 title in my view