Yeah, GWAR generally don't have a classic metal sound, but I'd be very much surprised if they didn't have at least one song that did have it, since they seem to dabble in many different metal subgenres (just off the top of my head there's thrash, surf metal, melodic death metal, and whatever genre "Think You Oughta Know This" was (horrorcore?))
At some point I'll have to read through this entire thread. Assuming though that at some point Probot has been brought up? Dave Grohl covered the styles of so many bands of my youth like Celtic Frost, Voivod, DRI. Not sure if anyone else has done a project quite like it...
Did a reread of this whole thread, and one thing that came to my mind after a discussion with a friend earlier; In Sweden we had a movement in the late 60's / early 70's called Progg (that should not be confused with the progressive rock from the UK and US). This movement here in Sweden went far left politically, whereas in other places it was more psychadelia. And when I say far left, I mean communist-types of left protesting what they though wwere a capitalist society (and we had at that time had a socialist democratic goverment for ages, and they were not considered leftish enough by these artists)...
Two bands that arent old school or even "metal" but are relatively newer are Bigelf and Kyng.
Bigelf is more prog-based but has alot of Sabbath, & Floyd influence without being contrived. They started in the 90's but didnt get much traction until the 2000s. Think they've disbanded sadly. Their CDs arent easy to find, but if you want to check them out I suggest starting with "Hex" circa 2002-2003 maybe. Saw them in a very small theater in 2009 or 2010 and they were awesome.
Kyng have 3 CD's out, all are good but their first "Trampled Sun" is their best IMO. They are doom/stoner metal with a Soundgarden bent, think they started around 2010. Again one of those bands that wear their influences on their sleeve without sounding like a direct ripoff.
I personally don't like categorizing music too much, I just look at it as good and I like it or it suck and I don't. Most musicians either hate the genre label they been given by the media and consuming public and when asked to classify their music will just say we tried to make the music we like and the best music we could at the time.
I have a friend I grew up with in Buffalo that played in alot of local bands. One, STEMM started getting popular along with Chimera in the early 2000s. Damageplan, Stemm and Chimera played a show in Buffalo Dec 7, 2004 and all three bands went and partied at the casino in Niagara Falls after. I remember my friend telling me how surreal it was to meet and hang out with Dime & Vinnie only to find out Dime was murdered the next day. He said it was just a testament to how cool and humble those guys were to take out a couple of young band partying as peers and not thinking they were any better. Hard to believe its been 16 years since Dimes been gone and 40 for John Lennon.