Bit over-rated, solely in the fact that as an allegorical film it doesn't hit just as hard as it's made out to, at least not for me. I don't identify with the characters personally, so couldn't take as much out of the film as some other people did. All characters started off as reprehensible and went from there, so you can imagine the character arcs.
Day Lewis is awesome as Plainview, the scene where he is watching the oil burn when he should be looking after his son is superb, you can actually see the greed in his eyes. His secret may be the way he lives his private life though, he's created a mysterious aura about himself that means we as an audience don't know who he is, and therefore allows him to throw himself into certain characters and thus make it much more believable than his contemporaries could. And Paul Dano is almost as good as Eli, he never really slips into the hokeyness that the character couldve forced. But the film as a whole isnt as good as its cracked up to be. It is good and it is entertaining, but not to the extent that the media are expressing. If the performances werent so special then the film would not have got so much attention. In saying that though, I was struggling to stay awake, so my perception may be a bit off. The bit where the old boy fires the gun to wake Plainview up actually woke me up too.
Its almost guaranteed to sweep the Oscars although.