What's up for grabs is whether or not There Will Be Blood is a great movie. I say it is, in spite of certain imperfections. Repeated viewing will reveal the movie more.
However, to take issue with your three parenthetical complaints, i.e:
1) Unbending characters, 2) Lack of women or any reflection of normal society, and 3) its relentlessness.
1) Horror's horror. We've had an unbending president, haven't we? Topicality does not make one great, but monsters such as Plainview (and Eli Sunday) have existed and still do, and are worth studying.
2) The Godfather
3) There's something to be said for burning even longer than you have the fuel for. The last 20 minutes of this movie are more surprising (and in retrospect inevitable) than any rain of frogs, a twist which I loved, you loved, and was ten times more of a reach.
It's still a pretty accurate description of the movie, Ebes.
And yeah, it's certainly up for grabs whether or not this kind of thing is enjoyable to watch.
But I've never seen anything like it, and that's been happening more often lately.