Ledger was a good actor, but the only reason he's a legend now for Joker is because he happened to pass away during post production. Otherwise, while the performance was an interesting take on Joker, it was an imitation of an older actor. I forget the name of said actor, but he even admitted it in an interview. The only reason he got the Oscar for Best Actor was because he passed away; it was completely unfair to the other nominees. He was not responsible for the heroin-addict like appearance that has been instilled in our heads since the release of the film. That is due to Nolan, Lindy Hemming (costume), and Peter Robb-King and John Caglione (for makeup). So again, he was a good actor, and he gave a very interesting take on the Joker, something completely unseen before, that did mesh well with the grungy universe of Nolan, but plain and simple, it really wasn't Joker. It couldn't be, he wasn't enough of a parallel to Batman, and that is Joker at the core. Everything that Batman isn't, Joker is.
So instead of remembering Ledger for this supposedly epic role of the Joker, let's remember him for the potential he wasted by overdosing, and that he maybe could have one day have become a great actor. It's such a shame he only became legendary because he passed away..
"Everybody tells tales . . . it's just the dead talk more quietly than other people."