It may be debatable, but I regard Tony Hawk 3 as the best example of the series. It features an astonishing amount of tricks and clever and original environments that seemed lacking to me in TH4.
One of the best design innovations in TH3 is the ability to earn cash and redeem it at the pro shop for new super moves. However, you can assign the super moves to whatever button combo you wish, so you are not forced to remember a strange series of presses while you are ollieing off the side of a cruise ship. This small innovation lets you play all the characters, unlock new super moves, and still know where they are all the time. TH3 has hours upon hours of pure gameplay.