I'd have to say that Lamb of God's vocals are fairly easy understandable. He's not screaming like As I lay Dying, I classify more like yelling. There are a few metal bands that have singers instead of screamers, some are great, but some really should have screaming vocals instead.

But yea, they are awsome. I saw them back in June with Bodom and Slayer, they're so awsome live. Morton and Alder have done lesson columns in Guitar World and recently have done 2 video lessons, one of which was how to play Redneck.