PGR2 is a game that all games should aspire to be similar to. It is vast in scope, with lots of cars and tracks to unlock; it has immersive gameplay and is easy to pick up but difficult to master. PGR2 has beautiful graphics and sound. In a lot of aspects it feels tighter and more intuitive than PGR1.
A big improvement is the decreased level of difficulty. Beating PGR2 at a Platinum level is still insanely difficult (and no I haven't done it) but now gamers can complete PGR2 at a bronze or silver level - much more accessible user experience.
The LIVE component of the game is the other huge addition that takes PGR2 to the next level. Playing over LIVE and interacting with other gamers is priceless. PGR2 has the seamless integration of single player with online gameplay; after each completed event the LIVE servers update the gamer's standings even though he/she is not playing online.
Overall - PGR2 is a very solid and good effort that will make you smile if realistic arcade racing is what you are into.
How come I don't give PGR2 a 10 in this case? In my opinion despite the above innovations and glitter PGR2 doesn't provide gameplay as pure, classic and pristine as PGR1 did. PGR1 took you by surprise and shook your perception of racing, and exploded your senses in the meantime. PGR2 takes that PGR1 vision and polished it a bit, but didn't provide the same amount of spark as PGR1 did.