Okay, let's get this out of the way first: This movie takes historical accuracy and beats it in the face with a 2X4 and gleeful abandon. But beyond that, how does it work as a movie? Considering the subject matter, and the studio behind it...surprisingly well.
First the bad: While they somehow managed to get a Star Studded voice cast for the picture, it's clear Disney had little faith in the project. The animation is below the DTV sequel level of cheap, with tons of reused shots, still frames, and barely there mouth flaps. Next, the third act is absolutely bizarre. I'm not talking about the fully choreographed dance number in the middle of a concentration camp (though that is a bit jarring) but rather the strange ending that feels ripped from a different movie entirely. It's clear the writers didn't know how to organically pull out a happily ever after from a Holocaust movie, and the film suffers for it.
But now for the good: remember that voice cast I mentioned? Yeah, it's pretty great. Madonna turns in a surprisingly earnest performance as the maniacal necromancer Sgt. Olga, and is easily the standout in the cast. Who knew she could do such a convincing German accent? Also, the musical numbers are a ton of fun. One particular standout is "I Used to be Ze Bad Guy" performed by, of all people, the Ghost of Kaiser Vilhelm. Another plus is the characters who, with few exceptions (Miep tends to be far more annoying that adorable) are well written considering the source material.
Overall, while Disney's Anne Frank falls flat on a technical level, and has some serious issues with the way it adapted the original story, it's not terrible, and certainly not the worst Disney has put out. I'd say it's worth at least a rental.