It's the story of a man and his young son during an oil strike in a remote area of California at the turn of the last century. (A hypocrite preacher-man is thrown in, too.)
I think Daniel Day Lewis (in the lead role of oilman Daniel Plainview) earned his Oscar.
His performance was the strongest part of the film, which was interesting and well-executed -- but I wouldn't rush to see it again.
I don't think this is the work for which Anderson will be remembered. My hunch is that will be his 1997 film "Boogie Nights," which was more human and compelling.