Rust abandoned his nihilism and accepted that life has meaning, even if he can't quite grasp what it is. He was also finally able to come to terms with the loss of his daughter.
Marty made peace with his estranged family and showed them that there was still good left in him. He also proved to himself and Rust, by finding the tiny clue that linked everything together, that he was indeed a "true detective" and not just Rust's secretary.
But what was with Errol’s weird accents? One minute he sounds like a hillbilly and the next he sounds like a Brit.
Yes to both.