The Melvins are just the Melvins. Whether you want to classify them into sub-genres is your own choice. The sad fact is that we somehow feel the need to categorize musicians/artists like this. Why? So one can say "I listen to punk music, cause I'm a punk, and punk rules, and you're not punk, and don't listen to punk, so you're not as cool as me"? What the fuck. Just dig whatever music you rock to, and quit trying to classify shit. Check out Wikipedia's bullcrap definitions of the doom/sludge metal genre of music. Might as well be a fucking new species of living organism. It's insane actually. Part of the reason I love the Melvins so much is their unique sound. Can't say I've heard anything like them. I'd actually go so far as to contradict myself above and create a new genre of music called Melvic. And the Melvins are the only band in the Melvic genre. I like Melvic. Do you listen to Melvic?
Sludge out with Melvic. Do it.