A shitty game? Sure ok. But a product that resembles nothing of what was advertised to the public many times, and completely broken to boot? It's false advertising.
Saying that the advertised game looks nothing like the actual game is a bit of an exaggeration. It definitely looks nicer than the actual game but again, that's always the case in marketing. Ubisoft is notorious for photoshopping all their screenshots. Just check out the official screenshots for Far Cry 3. Nobody's suing them for false advertising.
CM isn't completely broken, either. You can play the game from start to finish. Are there bugs? Sure. Is the game unpolished? You betcha. But it's not technically broken by the criteria that would merit a lawsuit.
As I said before, I'm not defending CM. I think it's a shitty game. However, I think this lawsuit is pretty absurd, given that its accusations can be applied to pretty much every game (or any other product) ever made. Why hasn't anyone sued Peter Molyneaux for all the crap he lies about? Why hasn't anyone sued Ubisoft for photoshopping all their screenshots? Why hasn't anyone sued Microsoft for making it look like multiplatform titles are Xbox exclusives by only showing their own logo at the end of TV spots? Why hasn't anyone sued Square for marketing their games using only pre-rendered cinematics? Hell, a lot of ads use CGI that isn't even in the game (like the Bioshock Infinite TV spots). The GameStop ads routinely use modified in-game assets to represent scenes and events that never actually happen in the respective games. I can give you a million examples of ads that are even more misleading than CM's and yet received no legal threats.
To single out CM amongst the sea of bullshit that has always been the foundation of marketing just seems silly.