While puzzling over the nature of instincts in Principles of Psychology, William James asks the rhetorical question: "Why do men always lie down, when they can, on soft beds rather than hard floors?" His answer is that this question is rhetorical - there's no answer. This is just what men do: "Nothing can be said more than that these are human ways, and every creature likes its own ways."
Nothing I can say about There Will be Blood is more revelatory than this: we see its protagonist Daniel Plainview (Daniel Day-Lewis) sleep on hard floors. He's a wealthy man, who could have any of his desires satisfied, and yes, does at times have a bed or at least a blanket, but we see him sleep on wooden floors. In other words, this is a creature who does not like the same ways as the other creatures we call humans. As Plainview would say: "these people." He's a man apart, a man with his own drives and his own (possibly inexplicable) desires, and his ways will never be clear to us, anymore than the ways of the squirrels will be clear to us. He is, at some point, simply not one of us "creatures" or "people," but something different. Something uber, perhaps? That's further than I can go right now.
Otherwise, I have little to add to the volumes that have already been written about the film. The cinematography is impressive. The dialogue is sharp, cutting, and practically tangible. The dissonant, nerve-wracking score, by Radiohead's Johnny Greenwood, may be the best I've ever heard (I've been trying to think of better scores. I like Hans Zimmer's for Gladiator and Vangelis' for Blade Runner. I might just like Ridley Scott). Plainview is played by Daniel Day-Lewis as a sort of oil tycoon version of Bill the Butcher, who does more of his violence to those around him emotionally, rather than physically, and yes, has probably given the best performance of anyone this year. And Paul Dano, the mute Nietzschean of Little Miss Sunshine, proves, as the preacher who Plainview takes a particular dislike to, to be a worthy foil to Day-Lewis' driven oil-driller. The movie's 2 hours and 40 minutes long, however, so you better go in prepared to spend 3 hours of your life staring at Daniel Day-Lewis, continually filthy, running roughshod over every human being around him, interspersed with stunning but bleak extra-long shots of Texas (standing in for California) wastelands and driven by an eerie, piercing score. If that doesn't sound like a good Friday night to you, I don't know what would.