The interface is simple yet brilliant, the controller setup is the most "tunable" I've come across to date, you can get just about anything to work, and you can adjust the game's settings to work with whatever you've plugged in.
There's a huge variety of cars to drive, from slow stuff on road tyres to twitchy GTR racers and single seat open wheelers on slicks.
The game is challenging yet fun, and from the point of view of creativiity, you can alter so much with a copy of photoshop, literally everthing from trackside hoardings to brake discs and driver gloves. Not to mention quite how easy it is to make your own paintjobs for that personal look.
Oh and in case you hadn't figured it out yet, there's a patch due out this month, which appears to be about to provide a Formula 1 race car to drive, and certainly gives a couple of new track combos and better tyre physics.