It is absolutely worth it. GA is easily among the best driving games released on last-gen consoles and PC.
I'm a pure Forza lover, and even I love GA. I think once you immerse yourself in the racing, GT6 might become a distant memory. This level of thrill and excitement, I've simply not experienced in Forza or GT. Codies really got it goin' here!
Can't say enough good things about this game, pick it up. Though we hope to see more hardcore physics in future, GA is a very good start, and things can only get better now that GRID II is history, and they *may be* looking into development on current-gen consoles. *Just speculation*
You asked about the sounds; they are top notch my friend! The only thing I wasn't very impressed with is the lack of adequate wind noise, and that menacing bark coming from the engine on throttle lift off. Everything else is there from accurate engine whine to the exhaust notes. Race and atmospheric effects are brilliant, so are the tire screech effects (some of the best I've heard in any game).
In short, everyone needs to experience this game, whether you're a pure simmer or a casual racing kinda gamer.
Exactly, you sum it up very well. There are several things I find GA doing better than FM and GT.