For starters, I wouldn't worry so much about classifying them, or other bands. At the minute, everything new sounding coming out that isn't blatently thrash, death, black, etc. and seems to vaguely conform to to themes in other bands music seems to get lumped into the metalcore genre, just like a few years ago with nu-metal. Personally, i cant hear any real kind of hardcore influence in Lamb of God, so wouldn't call them metalcore.
As for the actual music, I love em and do actually enjoy Randy Blythe's vocals. I can see why people don't like the vocals, and I've increased my love of them over the years, but then, within my group of mates, I know of no-one who liked Ozzy's vocals the first time around, yet we all love them now.
I've seen them three times now, last december at the London Astoria with Devildriver and last year at Download, both of which I loved. However, the best was, when never having heard a song by them, I saw them playing support for Slayer at the Astoria in 2003. Thought they were a fantastic build up for Slayer (especially considering 3 inches of blood were originally supposed to be supporting), really got me and my mates going.