The Omega Man is way better than Will Smith's version. The relationship didn't get built up so his self sacrifice was not earned at all. The Omega Man makes so much more sense. Will Smith's acting is spot on, but the movie can't hold a candle to The Omega Man. It is a poor CGI substitute.

Nolan himself said that Cobb walks away from the totem deliberately as the point is that he doesn't care whether it is real or not. What matters to him is that he is reunited with his family, making the ending a happy one even if the totem kept spinning.