I like the fact that there are many definitions of the Joker as movies are produced, and even the last one from Todd Philipps with Joaquin Phoenix is a different one from his older brothers.
For example, Tim Burton's Joker (played by Jack Nicholson) is kind of reassuring. His makeup is perfect and clean and his style definitely comic and cartoon-like, and above all, he has built a universe around him, made of art and colors. He is, in his delirium, a creative artist. Nolan's Joker (played by Heath Ledger) is terrifying : there is nothing around him, only chaos and a vague cynical memory of the world in which he lives He doesn't beleive in anything, there is nothing sacred to him. He is more like a nihilist destroyer than an idealist. All he want to do is to prove that darkness exists in everyone.
The fact that we can express hatred, sadness, foolness, and many other terms that define vilans in each Joker we create is really cool. Every director has its version of the Joker, and that's what makes me want to watch all these movies, again and again.