Oh, I find these guys to be just terrific. They started out in the early 80's, their genre was dubbed "Sludge" a precursor to Grunge. Kurt Cobain was friends with The Melvins prior to forming Nirvana, even auditioned to be their bassist, but was so nervous he couldn't play properly. Nirvana wasn't the only band they've influenced, many Punk acts, and Grunge bands such as Soundgarden apparently enjoyed listening to The Melvins. They've even influenced Tool and are personal friends with the band. "King Buzzo" lead singer/guitarist of The Melvins became a part of Mike Patton's (Faith No More, Mr Bungle, ect) super group Fantomas. Jello Biafra of the punk group "Dead Kennedy's" also did a Collaboration with The Melvins.
Their sound is slow, destructive and incredibly powerful. I'd suggest checking them out if you're into any branch of heavy rock music, or a fan of any of the bands mentioned.
Also, King Buzzo and I share a similar head of hair.