Batman: Mask of the Phantasm

Out of all the Batman films so far, including all the live action films, this one is still the only one to really explore the character of Bruce Wayne/Batman and examine what drove him to becoming Batman.

It has a great story that flashes back to just before Bruce took up the mantle of the bat and the woman he was involved with at the time, then skips forward to an unknown assassin killing Gotham City's mobsters, and we see how the 2 story's meet. The writing is top-notch, in no-way predictable and the voice acting by Kevin Conroy as Batman and Mark Hamill as the Joker truly amazing and bone-chillingly scary.

The only complaints is that the animation could have been better at some points, but that is because it was originally meant to be a straight to video release before Warner's saw what a masterpiece they had created, and also it should have run for a little bit longer, but oh well. If you haven't yet seen it i highly recommend it.