While he does a great job as the Joker, and I really like the new style Batman movies (vs. the cheesy "song and dance" versions from the past), I don't think that he was the greatest villian of all time because of Heath's performance.
It all starts with the writing, naturally, but I'd say his interpretation of the Joker, as written, was inspired. I thought they did a great job making his character interesting, which they still haven't done for Batman.
I never really cared about Heath Ledger. I liked him all right, at first, when he was in
10 Things I Hate About You, and then he seemed to have an attitude which I didn't care for, along with being in movies I had no interest in. Maybe his death has created a lot more conversation over his role as the Joker, but the conversation could have just as easily been, "It's too bad he didn't have a better final performance." It's some fine acting.
