The ending both both movies were great.
NCFOM didn't wrap everything up in a neat package, and it lost points for that with a lot of people, but I really liked it. It wasn't immediately satisfying, but it leaves a lot of interpretation for the viewer. Tommy Lee Jones' descriptions of his dreams gave the movie enough closure in my mind.
The ending for TWBB was equally as awesome. You could see Plainview's eccentric tendencies snowballing during the entire film, especially the last third. He is a man who is very protective of his appearance. He banished his "son" when he becomes an embarrassment, and only takes him back once his sending him away becomes more of an embarrassment. Plainview's attack on Eli was in part a retaliation for the embarrassment that happened in the church many years prior.