Well let's start by making this plain and simple: if you loved either of the previous Tony Hawk Pro Skaters (as most of the world did) stop reading and go buy this game.
For the fifteen or so of you that haven't tried a Tony Hawk game before, let's get a bit more in depth so that you'll know why you should go buy this game. I will start by saying that I am a role playing game fan, which also makes me a huge Final Fantasy fan. I've never been interested, even slightly, in skateboarding myself; in fact I don't care much for most sports. Despite these things, I love this game.
Pro Skater has a fun blend of adventure and mission completion and delivers this in a package that allows us to do tricks that 99.9% of us will NEVER do in real life. They serve up this adventure and mission completion by giving you a list of tasks to complete in each of the sprawling levels. They will be as simple as performing a specific trick in front of a photographer that is stationed somewhere in a level, or as complex as stopping a police chase. Once you get the hang of the controls (which may take all of 20 minutes) most of the tasks are easy to complete. For each level, there are more difficult tasks and they keep the game from being a breeze.
Now I did mention the tricks before. The trick system is unbelievably easy to use and allows each skater to do 8 of each basic type of trick (i.e. lip balance, skateboard flips, grinds and grabs). While doing these tricks, you build up a "Special Meter" and once it's full you can pull some huge tricks like the 900, that's a full 900 degree spin. A great part of this trick system is the fact that it's completely customizable. If your skater has a grind trick that you think is lame, you can replace it with a cooler grind, and as you progress you can add more special tricks to your repetoire.
Throw into this mix an awesome hip hop and punk soundtrack and beautiful graphics and you'll find that you just can't go wrong with Pro Skater.