Yeah, I feel a little that way. There's only really one gymkhana arena, and Codemasters missed out on a heap of tricks - like driving on two wheels, reverse spins and donuts, and even grinding on a rail (which Block did in Mountain Lab 1.5, the first video).
There's talk that Codemasters could make a gymkhana-only game next (I've heard rumours that DIRT 3 will be the last in the DIRT series), which would probably play out like a skateboarding game. If that's the case, then they'd really need to expand things to include more arenas the size of the Battersea Compound. With Gymkhana 4: The Hollywood Megamercial being released overnight, I could see them adding in the Universal Studios backlot as another location, as well as the Port of Los Angeles and Monthery-de Linas from GymkhanaTwo and Gymkhana_THREE - Ultimate Playground. And possibly the airport and aeroplane graveyard he took James May around for Top Gear. But even then, that's only five arenas. Games like Tony Hawk's Pro Skater (particularly the second game in the series, before it got bad) had upwards of a dozen skateparks. And they had a multitude of tricks in them, not just the four in DIRT 3.