I would first like to say that I have played the original Skate (and clocked it) and was therefore was a little worried as to what they would be able to improve on. But these worries were not justified at all, as having now spent a good many hours playing through Skate 2 I am really impressed with the improvements. The whole package has been tweaked and adjusted and there are are a huge variety of new tricks to try. Hippie jumps are now possible( if a little hard to master) , and you can also preform handplants, fingerflips and various new grabs ( One-foots, Judo airs, Airwalks and Superdudes are my favorites).
The sandbox environment has been expanded, and incorporates new areas of San Vanelona for you to explore. The security has also been beefed up significantly in some areas ( mainly downtown) , and there is nothing cooler than skating through buildings and grinding down rails with 4 security guards chasing you.
Even though this game is hugely entertaining, it does have some points to it that aren't so good. You will need a lot of patience and a fair bit of luck to progress through a few of the challenges. It took me at least 150 retrys at a particular challenge before I finally pulled it off, and some people will get frustrated with this. Also, some of the trick contests are held in areas that are too cramped or don't have enough objects to trick off, and there are a few minor niggles with some of the new tricks (gapping up to a rail and then performing a handplant is a bit iffy).
But these problems are insignificant, and really do not detract from the game at all. If you liked the original Skate then you will totally dig this one. And for new-comers, I recommend it highly.