Batman: Gotham by Gaslight is an atmospheric detective thriller with genuinely clever twists and a wonderfully crazy storyline written with immense skill.
Batman Beyond: Return of the Joker is a stunningly crafted animated film brimming with personality, a deeply interesting story, and amazing vocal performances.
Batman: Mask of the Phantasm is one of the greatest Batman stories ever told. It's a stunning piece of animation with a story that is equal parts gripping and unpredictable.
Justice League: Throne of Atlantis may not offer a gripping story or a great villain, but it does offer fun superhero action with a good sense of humor.