These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: There Willbe Blood
Alternate Character Interpretation: Most people interpret young H.W. as a good little kid trying to be the best (adopted) son he can be to Daniel. However, in one profound way, one must wonder if a little of Daniel's psychotic nature has rubbed off on him. Remember how H.W. tries to kill the impostor posing as Henry Plainview by setting his bed on fire? Granted, he was right to be suspicious of the man, and he was likely trying to protect Daniel, but even so that is still a pretty awful and insane thing to do. And sure, H.W. is young, but he is definitely old enough to know that fire is dangerous and can kill people, especially considering his adopted father is an oil tycoon. Plus, based on how the event is shown, if the fire got out of hand, H.W. could have gotten the impostor, Daniel, AND himself killed. Thankfully, this issue seems to have been resolved by the time H.W. becomes an adult.
That's if you think the purpose of the fire was to kill Henry. It's also possible that it was simply a cry for help from a young boy terrified of a future he can't understand and unable to communicate that fear or receive reassurance from his father.
Daniel Plainview: How evil is he? Is Eli better or worse than him?
The third movement of Brahm's "Violin Concerto in D" is used twice in the film. The second time it serves as the music for the credits, which obviously occur right after the ending. The Soundtrack Dissonance alone makes it excellent.
Misaimed Fandom: Despite the fact that Plainview is most commonly seen as a monstrous psychopath, and that the dominant interpretation of the film is as a condemnation of people like him (or rather the politicial/societal climate that enables people like him to succeed), a decent portion of viewers related to (and supported) Plainview.
Granted, it's easy to root for Plainview when he's put up against someone as unlikable as Eli, however these viewers seem to ignore that the point of the film is to show the moral degradation of Daniel. This is especially glaring in regards to the ending of the film, a number of viewers seem to think that Daniel's brutal murder of Eli is a good thing, and is meant to represent the ultimate triumph of Plainview, despite his last line of "I'm finished!" is blatantly meant to represent that the opposite has just transpired, and that he'll be headed for jail or a mental ward now.
Narm / Narm Charm: Splits the opinions of the milkshake lines even further.
Eli's sermon where he "exorcises" the arthritis from one of his parishioners manages to be both ridiculous and disturbing at the same time. In particular, the bit where he says that if he loses his teeth he will "gum" the ghost would be laughable if he didn't have his group of fanatics believing every word he says.
Henry not dying straight away despite a bullet in the brain is pretty damn disturbing.
It's intriguing that most of the nightmare fuel comes from the soundtrack playing over what are mostly pastoral landscapes in West Texas. On multiple viewings, though, the nightmare fuel shifts to being Daniel Plainview himself.
As mentioned above under Narm Charm, Eli's exorcism ceremony would be laughable except for the fact that his parishioners are fanatically hanging on to his every word, making the scene really creepy.
The entire last scene. No matter how much you dislike Eli, it's still very unnerving to watch him first be reduced to groveling and tears, then to be chased around by the obviously furious and likely insane Daniel, unable to escape the room, then being bludgeoned to death as he begs for mercy. Yikes.
One-Scene Wonder: Real life deaf actor Russell Harvard delivers a short but impressive performance as adult HW.