Tony Hawk Undeground is the place to start for people who have never before considered the serise. Finally it's geared towards everyone, of all skill levels. You can play on many different difficulty levels, which is great for pick up and play gamers.
What really impresses me is the controls. Often, when you can do so many things in on game, the controls become aggravating. That's not the case with T.H.U.G. Playing it quickly becomes second nature, and the new walking feature handles better then I expected.
Finally being able to get off the skateboard bring new life to the serise. It also make combo possiblites near unlimited. You can reach places you never could before and create your own trick to do once you get there. Nice!