There seems to be a huge number of negative reviews for this game on Amazon, and to be honest, I can't really see why. Having played this game for a while now, I have never found myself frustrated by it; the controls are nice and responsive as far as I am concerned (using the classic controller), feeling like you're actually driving on a proper, loose-dirt road; graphics are just fine for a Wii game (don't compare them to the PS3 or 360 versions, it's an utterly pointless operation) and the sound is nice and chunky.
Most of all though, this game is FUN! The challenges are good fun to play through (particularly the air challenges, where you have to get your car airborne off a series of ramps strewn around each track for set amounts of time to be awarded a medal) and, for once, I've even gone through the time trials on each course trying to improve my best times.
The cars do handle slightly differently in my opinion. This isn't a simulation of course, so don't expect truly accurate handling but there's enough variety here to keep you interested in unlocking new vehicles. The tracks too are all sufficiently different (although not really very long), each offering a slightly different kind of challenge to your racing ability.
Overall, if you treat this game like an arcade racer, you won't be disappointed. If you're looking for simulation, go buy Ferrari Challenge: Trofeo Pirelli (Wii)
instead (ironically, there are people reviewing that game that complain about it being too much of a simulator!) Dirt 2 for Wii is what it is, and what it is, is a great fun rally racer that can offer as much in a short burst as it does in the longevity of the challenges and seasons it provides.