Holy Retro Animation, Batman! The Mask of the Phantasm is certainly a blast from the past, with clear connections to the animation styles of the late 80's and early 90's Batman TV shows I grew up with. Unfortunately, the plot suffers a little from similar dating, never quite managing to break out of what are now trope-filled contours and predictable connecting sequences.
Still, the overall result is an enjoyable stroll down memory lane, to a time when Batman was a little less nuanced and a little more sexist; when the Joker was nothing more than a crazy gangster; and before years of continuity had weighed the franchise down. The titular Phantasm was a fun character, though suffered most from predictability, with abilities that are never really explained. The side cast are largely forgettable, with an exception of Alfred, for whom a step back in time enabled frequent attempts at cheesy 90's cringe humour. The gags fall a little flat, but they're endearing in their attempts.
Most interesting was the rapidity at which Gotham turned against their resident hero, resulting in a realistic and almost fatal confrontation between the cops and Batman. Here, the lack of mythology surrounding Wayne enabled some far more interesting storytelling with higher stakes than would be possible in a modern equivalent. Today, armed with a multitude of impossible gadgets and superhuman intelligence, such a contest would feel distinctly one-sided.