Pulling off a Level 2 Power Play and taking out nearly the entire grid in one blow.
Jumping over all other cars after a particularly long jump, staying on the lead while dodging falling cranes and cars set aflame like a lunatic, stylishly finishing off a stunned opponent by ramming him against some crates...
Surviving a Level 2 Power Play. Considering a Level 2 Power Play is something of a Limit Break, speeding away from one unharmed can make you feel like a Determinator on wheels. Bonus points if you escaped by the skin of your teeth.
Getting certain achievements are MADE of this:
Zero to Hero: Wreck the ENTIRE GRID, and make your way from dead last to first, with one Route Changer Power Play. Taken Up to Eleven if you get the specific ones like Frequent Flyer, or Swept Away.
Season Champion: Win the Split/Second Season Championship. This WILL make you feel like a Badass Driver, with only Perfection (win EVERY EVENT), being more awesome.
On a Meta level, the fact that Disney Interactive Studios, which usually made movie tie-in games of varying quality, came up with such an awesome game not based on a previous IP...kinda like the Disney theme parks of yore.