First: don't wait for DVD to see There Will Be Blood. Its overwhelming physical intensity will lose a lot on a small screen (no, 56" LCD in a home theater won't cut it.)
Second: Its inspiration was Upton Sinclair's novel Oil! , about a California tycoon and his son. Well, yeah but... that's misleading in that Sinclair's rep (90% from The Jungle and whatever we recall of "muckraking") brings to mind Progressive social/political reform and big-picture historicity. There Will Be Blood does portray a very convincing early-20th-century California. But what it's about is Daniel Day-Lewis's character, in the same sense that Citizen Kane is about Kane's. It's not irrelevant that Kane (and William Randolph Hearst) were newspaper tycoons, but the energy of the movie comes above all from a central figure who wants. Wants... something? Everything? That he doesn't know is part of the fascination, but you'll damn well know -- feel -- that whatever it is, he wants it more than most of us have ever wanted anything.
Ditto for There Will Be Blood: real blood, bloodlines, the Blood of the Lamb, and oil as the earth's blood make a rich and artfully exploited thematic mix. And it does matter that we bring to the movie a 2008 awareness of just what a big spike in the arm petroleum has been for the modern world. But it's possible to imagine this character and his story, like Kane's, set in another time and place and industry.
This is a great movie at a whole nother level than 3:10 to Yuma is a very good movie. My admiration for the latter is about craft and polish. I'd seen all its components used before, but they're exquisitely fitted, and the performances -- several of them first-rate -- are subordinated to that. In There Will Be Blood, although Anderson's craft is everywhere, "polish" is the last word that comes to mind. Is an earthquake or a heart attack polished? Day-Lewis eats the screen alive, sucks the air out of your lungs, takes you places you've never been, maybe places movies have never been.
Stop reading. Check your local listings. Go.
[Update: when I saw Day-Lewis as glass-eyed, blade-fondling Bill Cutting in Gangs of New York, it occurred to me that Leonardo di Caprio -- the nominal star -- would be well-advised to buy up and burn all the prints, because when he shared the screen with DDL he might as well have been invisible. Well, any other actor or director who wants an Oscar this year should do the same for TWBB...]