I pulled up Heaven and Hell and gave it another spin this morning. Much better than I remembered! Solid rock and roll, great riffs, and of course Dio's voice. I'm on my second spin right now.
I think at the time, it was just too different, too much "not Black Sabbath" (which at the time meant everything up to that point). The doom and gloom of their original sound was all but gone. Still heavy, but not all dark and dreary like the early stuff. Some of it reminds me of Deep Purple.
In 1980 I had already dived headfirst into prog, so "basic" rock and roll wasn't doing it for me. I remember listening to this album and thinking it was nothing special at all. No Ozzy, and it's so much lighter that it almost sounds happy, which is not Black Sabbath. Today, I can look back and appreciate things more for what they are, not dismiss them for what they're not. Funny how that works.
Sometimes I'm a bit jealous of people who get into classic bands long after the fact, and the thrill you can get when you first encounter something great. And there's also a perspective you get that obviously isn't possible if you're there as it's unfolding.