The Melvins are highly regarded as a huge influence upon the sludge and drone genres. The band's genre fluctuates from release to release, playing grunge, stoner rock, drone rock, hardcore influenced rock, or experimental pieces.
That's what MA says. Basically, all their albums are different, sometimes giving or taking influence from a certain style, sometimes jumping to completely new genres. Well, this one's a sludgy one. In fact it's one of the first sludge albums, along with the early releases of Crowbar and Eyehategod. It's a classic, so you should already have it. If you don't, get it. You'll like it.
