KISS. KISS. KISS!
Was there a better hard rock band in the 70s then KISS? I think not. They released stunner after stunner after stunner of amazing hard rock that only AC/DC could rival in terms of sheer balls-to-the-wall guitar power. I could sit here naming classic song after classic song, from "Love Gun" to "Detroit Rock City" to lesser known but equally as fantastic songs like "I Stole Your Love" and on to the slew of "solo" albums KISS released in the late 70s (featuring Ace Frehley's infectious "New York Groove") they simply could do no wrong.
Until they took the face paint off. I could deal with the disco-rock of "I Was Made For Lovin' You" as that wasn't a bad song at all. But when they took the make-up off and decided to play your generic MTV-bound hair metal of the 80s they died in my book. Psycho Circus was no better as well.
Not a big ELP fan. I recognize their musical accomplishments and respect them, but I've never been a very large prog-rock fan. There's experimental, and then there's just wasting a listener's time.