I've tried to get into metal, but I have a hard time when there is no discernible melody or harmony. Not to say I don't enjoy a lot of dissonance and atonalism in music, but my problem with a lot of metal is that even those qualities like dissonance and atonalism tend to get lost in the audio mix and it all ends up sounding like a sludgy wall of noise. So for those, I tend to go to post-rock, proto-punk, kratutrock (i.e. Can and Neu!) or other genres. There are exceptions--I can enjoy some proggy metal like Tool, I like classic Metallica, who did a good job balancing the quiet moments with the crunchy loud moments, early Sabbath (which I define more as hard blues than as metal--the logical continuation of what Cream started), and I like a lot of borderline metal bands like Deftones and Failure. I like Motorhead but to me they are more in the realm of punk and hard rock than in true metal.
Have you tried melodic death metal? Some of it can be quite a bit more dissonant than all the bands you've listed, but a lot of the bands utilize quite nice melodies when they have talented clean vocalists, and balance both quiet moments with louder moments.
I'm kind of immune to dissonance/atonalism so if these recommendations don't fit what you're looking for, I'm sorry.
(They have longass songs, but they're a metal band that's often respected by non-metalhead music lovers.)
(Not my favorite song of theirs, but they're my favorite melodeath band, and this is one of their "catchiest.")
(OP posted this in the first page already, but I will always promote Insomnium.)
Also, many bands combining female and male vocalists do a lot better with utilizing melody while maintaining a dark sound. (Draconian, at the top of this page, is a good example.)
Finally, based on what you've said, you'd probably like a couple of other metal bands that started in the 80s. That's not really my genre of expertise but there's a lot of good thrash, here's some I like.
IDK why I put effort into this post, I'm very bored right now, hopefully something here is of value.