Pretty good; far from great.

Maybe the fact that I played Company of Heroes right before C&C 3 biased me. Heroes was challenging and fun. C &C is neither challenging nor all that fun. 90% of all missions are basically the same. Destroy building X by one of 3 methods: 1) superweapon (when available) 2) tank rush 3) sorties.
The maps are small and missions are short, with the exception of the final few in each campaign. Graphics, musics, and sound effects are unimpressive.
Hm, so what does this gave have going for it? The cut-scenes are corny and melodramatic...BUT, you can't help but love the cast, and so, you do look forward to completing missions to see the story evolve.
Remember the original C&C? Sigh. If only C&C 3 had 1/3 the thrills.
Bottom line: if you are a fan of C&C, how can you not buy it? I simply suggest waiting for price cuts.