Since when was Lamb of God not metal? They're most certainly not nu-metal.
I'd put them in the same class as Slipknot, need I say more. Chris alder is overrated too, considering a lot of his fast double kicks were recorded at half the speed as they sound on the album.
You clearly haven't seen Lamb of God live - if the kick beats are recorded at half the speed as they're played on the album how does he perform them live? I saw it and heard it with my own eyes/ ears and he most definitely plays the songs exactly the same live as on the record.
They were stunning live, got the crowd going better than most bands I've seen. DevilDriver who supported, similarly, got the crowd going brilliantly, and I don't even like DevilDriver.
To say Lamb of God aren't metal is ridiculous, rock bands don't sound the same now as Sabbath did back in the day for the simple reason that rock has evolved. Metal, too, has evolved (which is why I guess that stupid banner of New Wave of American Heavy Metal came about). Much like any other genre of music, pop, jazz... you name it - stop getting so anal about what "proper" metal is, to be honest it just makes you come off as narrow minded, and I'm sure you're not, I'm sure you're just voicing your opinion, but to write Lamb of God off as not metal... hmmm... personally I don't like As I Lay Dying all that much but I wouldn't consider them "not" metal.
My personal metal favourites are Danny Carey and Chris Adler, along with a host of others, Chris Pennie being the main one that comes to mind.