KISS rocked hard enough. Unfortunately they are remembered for crappy songs like 'Rock 'n' Roll All Nite' and 'Shout it out Loud'. They have plenty of rockin' tunes that I would definitely classify as metal (Parasite, Almost Human, God of Thunder, Goin' Blind, Black Diamond, 100,000 Years...). It was, after all, the 70's.
KISS went downhill way before they took the make-up off though. Anything after the solo albums, up to the time they took the make-up off, was pretty much disco(the only reason I don't include the solo albums is because Ace Frehley's rocked). Disco Bad! I don't care for anything they did in the 80'sThe Revenge album had a couple high points, and is probably their best non-compilation album since Ace Frehley's '78 solo album.
All in all KISS has sucked more than they've rocked. However, when they did rock, they rocked pretty hard, so I still dig 'em.