So I'm listening to a bunch of early David Byron fronted Uriah Heep the past couple of days. In their worst moments (which are still sort of fun) think Spinal Tap's Stonehenge with less self awareness and dopier lyrics (ex. Rainbow Demon, The Wizard). At their best (ex. Circle of Hands, Easy Livin', High Priestess)they came up with some of the best, utterly over the top progressive hard rock of the era.
Unfortunately, they started going stale after five or six albums, fired the alcoholic Byron and later morphed into a straight forward metal band with albums titled wretched things like "Abominog" (cue spooky music).