I never saw "Ulee's Gold" so I can't comment on his Oscar-nominated performance in that film, but I was never impressed by any other of his performances that I did see.
Easy Rider was such a seminal film that I'm not sure whether or not it needed a great screenplay. I do know that it made a huge impression on me as a 15-year-old budding hippie, but really all that I remember from it was Jack Nicholson's performance and the final scene where the redneck with the goiter shoots Dennis Hopper.
He really was not as good an actor as his father or sister.
Regardless of any artistic talent he may or may not have had, he proved to be either mentally ill, an out of control alcoholic, or a despicable human being (probably all three) when he tweeted:
Can't wait to see a Fonda fan defend them.
Still, he was a fellow human so I do hope he is resting in peace. God forgives.