I was lovin' Skate 3 until it started freezing on me every 20 minutes in create-a-park, and considering Skate 2 was essentially an add on to Skate, the word "quality" comes to mind.
But really there's not much you can do with a skating game, except build new places to skate in. This will satisfy the small core of people interested in buying a skating game, but it's hardly something that will help gain an audience.
As noted by others in this thread, letting more time pass between releases might have helped, but I'm not sure how much.