Two race styles repeat throughout the game: standard and drift. Complete the bulk of them within any one circuit and you unlock the next, as well as the chance to earn new cars (which you can then customize with new bumpers, hoods, side panels and artwork you design using the DS stylus).
Ignore what we said about Juiced 2 possibly being your game even if you don't like drifting. You can't avoid it. The drift challenges are actually one of the most compelling reasons to play. It's all about risk versus reward. Take every corner at a crazy angle, sliding from one to the next like a man possessed. You'll do really well. Play somewhere that's profanity-approved, though, if you tend to panic any time you're near a railing. Either that, or plan to buy earplugs for everyone within a 200 yard radius.