Curtis made a lot of movies. The ones that remain truly memorable can be counted on the fingers of one hand. In some of those- Spartacus for instance- he struggled against miscasting. He wasn't one of the greatest stars. The great stars last. His cocky machismo is of its time and soon went out of fashion.
I gather he was a nice guy. He knew he was lucky. He rode his luck. When the film roles started to dry up he reinvented himself as a painter. He went through addiction, came out the other side, and had too much character ever to go "poor me". Pick any of his later interviews and they're remarkable for two things, firstly self-knowledge, secondly, gratitude for all the chances he'd had. He could act shallow better than anybody going, but in real life he wasn't.