I've personally found most racing games on the iPhone to be seriously difficult to control, with the steering controls sending me veering back and forth across the track with no chance of winning. NFSU feels tighter, with a quick twist of the iPhone putting you into drift mode rather than sending you careening across the track. I actually got the hang of it pretty quickly. You accelerate automatically, with one finger anywhere on the screen acting as a brake. A quick swipe up is a nitro boost, while a quick swipe down puts you in Speedbreaker mode.
The graphics are really solid, with no noticeable framerate hiccups and reasonable load times. They're easily as good as the graphics you'd expect to find on the PSP. The music is a bit too aggro for my taste, but your mileage may vary. Overall, it's definitely one of the best looking games I've seen on the iPhone.
The game has a storyline that involves standard-issue undercover cop stuff that has you infiltrating a street racing scene that has vague ties to smuggling or some such activity. Full-motion video comes up between races to move the story forward via mediocre acting, but they never quite explain why cops actually arrest you when you yourself are an undercover cop. In any case, the trials where you need to take out cop cars are much more difficult than regular races, as they make you both ram cops and beat time limits, which was hard for my lousy-driving ass to do. There are 8 different modes overall that you'll encounter throughout the game, keeping things nicely varied.
There's a good amount of content here, with many races and game modes and a system in place to buy newer and better cars as you advance. It doesn't feel like a half-game made for the iPhone, and you could put many hours into this thing if you're a completist. For fans of racers who are looking for a solid game with good graphics and solid controls, this one is definitely worth the scratch.