Hmm.. IMO Heavy music has to have a creepy feeling that makes you feel paranoid (black sabbath's first album).
I don't see how can fast music be really heavy blahblah fffuuuu i can't talk or write this time of day anyways here's the heaviest song ever for you thankslol
I like heavy, extreme music, but anything which sounds too cliched just misses the point for me. There needs to be a level of experimentalism going on which really puts you out into unknown, untested waters. Maybe being a musician, I'm kind of just reading off chords to music which I find overly simplistic and therefore I tend to find it boring. Three chord rock drenched even in the heaviest distortion is still three chord rock underneath all the bluster. That was the problem with a lot of punk rock.
Here's an example of the kind of thing I really get into.
Ironically, this starts off as a kind of three chord thing, but there is a magical moment in this music that still amazes me even today, it's like the music breaks free, becomes alive, becomes almost funny, like some demented country music riffing in hyperspace.
When you're talking about heavy, imagine that this music was created basically in a sealed concrete cube slab, with multiple amplified instruments (some are not really guitars but custom designed instruments, more like amplified harpsichords with custom tunings) at about the loudest possible volume you could imagine or deal with. Yep... heavy.
You don't get composers like him any more, who can bring a combination of an encyclopaedic knowledge of harmony and a kooky, idiosyncratic style like that to bear on popular music. The old bop dudes blow my mind.