Sinner was the first album I listened to (partially). For the most part the singing is reasonable and the guitars and drums are decent. There's not much to object to, but aside from Bodies most of the songs are really fairly average.
Secondly, I listened to a bit of the Lamb of God album. I enjoy playing their song, Laid to Rest, in Guitar Hero II. The actual song is decent. The rest of the album, however, has the same sort of Cookie Monster singing, which can sometimes be alright and sometimes I get tired of it really fast.
The last album was City of Evil. I listened to the whole album. I'd probably rank Beast and the Harlot as one of my favorite songs off of Guitar Hero II, and the rest of the album is pretty good as well. The one flaw is that the singing seems to be relatively "modern" in style (read: vaguely tinged with a whiney emo style), but not so much as to detract from the enjoyment of the songs.