Sleep were quite clearly indebted to Black Sabbath at this point, and tried very hard to imitate their styles, much like Earth and Sunn O))) so it's not hard to hear why it sounds like it could have been released yesterday. Thick droning basslines and growling guitars are the order of the day, if you've heard Om then you'll know basically what to expect, but Sleep were always more Metal, they always had a bit more in the aggression department.
If you've been lapping up the recent slew of Earth represses then this should be marked as an absolute classic in the doom/stroner/drone metal genre.