Harrison Ford as Han Solo is less fun to watch than he is to remember. For me, it isn't about the actor/character of Han Solo as much as it is the idea of Han Solo as the underdog self-interested yet caring rebel with the sharp wit and cynical outlook that came from a difficult youth. Old Han Solo wouldn't be interesting, but, beyond that, he would break the idea of Han Solo.
For my money, Nathan Fillion as Capt. Malcolm 'Mal' Reynolds was a better Han Solo than Harrison Ford ever was.