I love this movie and is easily one of the top movies of the 2000's. My favorite scene is when Daniel Plainview has to go to the front of the Church in order to repent his sins.
When Daniel has to say that he abandoned his child the third time there's so much emotion when he says "I'VE ABANDONED MY CHILD", that its real, its not him trying to fake his way through the baptism but for a brief moment you see his actual self. The camera is still concentrated on him, right on his face with only the hands of the preacher entering the frame. Yet when the preacher starts to slap him and go with his antics of casting away the devil Daniel reverts back to his amused look (with the camera taking a medium-ish shot of both actors) as he successfully duped the Church and the preacher. He's almost laughing as he says "Yes I do" Another highlight is when the oil rig explodes which I thought was a visually beautiful scene: Last thing is that it could be seen as an epic movie because it has the perfect parts: an astounding actor, a great director, great soundtrack, beautiful cinematography and so on. Because of this I liked Roger Ebert's (RIP) take on it: "I am not sure of its greatness. It was filmed in the same area of Texas used by "No Country for Old Men," and that is a great film, and a perfect one. But "There Will Be Blood" is not perfect, and in its imperfections (its unbending characters, its lack of women or any reflection of ordinary society, its ending, its relentlessness) we may see its reach exceeding its grasp. Which is not a dishonorable thing."
http://www.rogerebert.com/reviews/there-will-be-blood-2008
My own interpretation of this is a little different, i think Daniel has a momentary realisation that sending his child away was the wrong thing to do because it reflects badly on him in the eyes of others. From the time he adopts HW he uses the child to get deals with landowners impressed that he is a 'family man'. HW is an asset and a means to get what he wants, i think in this scene he realises he shouldnt have sent him away for that reason. Daniels driving force is his need for power, when the time comes later he casts HW away again when he has achieved what he needs and has no further need of him.When Daniel has to say that he abandoned his child the third time there's so much emotion when he says "I'VE ABANDONED MY CHILD", that its real, its not him trying to fake his way through the baptism but for a brief moment you see his actual self.