Skate 2 is a very good game. It surpasses the previous title holder of "best skateboarding game on the planet," Skate 1, but only by a small margin. The new tricks do add quite a bit to your lines, but only if you choose to work them in. It does not revolutionize what Skate did well, but Skate 2 polishes everything up a bit -- the exception being walking, but even that is an improvement over being glued to your board. The online play in particular is a significant upgrade over the previous version.
Skate 2 is every bit as good as Skate, and in some ways better, but it is not a title that you can point to and say "this is as good as it will ever get." However, for now, it is as good as it gets.