Well, I think the last Tony Hawks game I played was TH3 years ago, when I was in a game store recently, they were playing this on the test machine, and I was hooked!
Firstly, the game has developed so much since the earlier games, there's more complication, sure, and there are more tricks, and more technical stuff, but that's fine, it's more of a challenge than a hassle. The graphics are superb too, really lifelike, although the ragdoll physics do tend to make amateur dramatics over some bails (since when does falling off a curb send you flying over a building!?) but they're more entertaining than a problem.
The game is difficult though, there's amateur, pro and sick achievements for almost every goal, and the sick goals are almost impossible to do! (for me that is), but once I've maxed my stats out a bit, I'll go back! Which is the beauty of this game! You can always go back, it's awesome.
There aren't enough bad points to even bother listing, so I'm gonna go with...it's too difficult, hah that'll do! It's an amazing game though, die hard fans, and newcomers alike won't be disappointed! :D