Something I don't particularly care for is Slayer's
Raining Blood. It isn't exactly awful on the scale of "mangled noise", but it does illustrate the beginnings of some concepts I'm not a fan of in heavier metal music. For instance, parts of it have no real discernable melodic progression and are instead basically just spammin' power chords. The singer's vocal style makes it difficult to discern the lyrics as well, and while the words themselves aren't exactly something I'm crazy about I've never really let the lyrics themselves turn me off from particular music.
There are also points in the song where I can clearly hear a melodic progression coming through, and that's not terrible at all, but there are points where I'd just as soon turn it off as keep listening. I'm sure you can probably extrapolate my concerns to the heavier genres of metal than that song represents for exactly what I'm not a fan of. I've give you a link to them but I'd have no idea what to search for as it's not really my preferred genre.
