Before I get going: this game is a faithful simulation of the 2008 NASCAR season. NASCAR races, with a couple of exceptions, take place on ovals, so to criticise the game because the idea of racing on ovals doesn't appeal to you is, to say the very least of it, curious. Not into turning left a lot? Move on, this isn't for you.
If you are into turning left, though, NASCAR 09 is a cracking racer. Graphically it's not Gran Turismo, but then NASCAR 09 is displaying 43 cars at a time and does a very good job of that. There's no slowdown, some excellent spot effects and the lighting, particularly as the sun sets (the sun moves through the sky as you race, so even in a day race the shadows will lengthen) is generally excellent. The twitchy controls and hugely aggressive AI of NASCAR 08 are gone, and in their place are much more precise steering, throttle and brake inputs and AI that races, for the most part, cleanly and fairly.
Wrinkles? As other reviewers have said, the game is incompatible with the US release, so no racing the Americans online, which is ridiculous when you consider where NASCAR races. The road course AI has hotspots on each track where it'll cause a caution every couple of laps (the downloadable Montreal being an especially trying exercise in frustration), and there are a couple of tracks where you'll be unbeatable once you've got somewhere close to maxing out the performance points you can apply to your car. In spite of that, NASCAR 09 is worth at least a rental for most, and should be an instant buy for those with a real interest in US motorsport.