With me, it was that I never quite realized how musically talented and intricate Mercyful Fate/King Diamond was (still is, I imagine).
Of course, even the "lighter" stuff was pretty kicking. But then again, I'm an 80s metalhead at heart.
(and I *swore* I'd never start going into the "well back in MY day..." thing with music!)
... and we're rapidly going off-topic...