It's very much a series of excuses to run Batman and his rogue's gallery through the alternative universe filter, all strung together with a reasonable plot, sprinkled liberally with japanimation tropes and artstyle, and best served with a suspension of disbelief. (And a tolerance, if not love, of japanimation.)
It's not perfect, but it hits far more than it misses, and is a strong contender for one of the better animated Batman films I've seen. (Or non-comic Batman media in general)
The animation is CG, and at times it's a wee bit fast, but it was a stylistic choice that was worth the cel-shaded effect, and sometimes it is damned smooth.
As always, it's the villains that make a DC story stand out; Joker steals the show, as usual, and the costume design for the other villains present is a delight to behold, even if they don't get to talk as much as Joker does.
The allies, unfortunately, didn't go down as well; they're more there as a deus ex machina / motivation point for Batman, in lieu of Batman's total lack of prep time, and come off as a wee bit self-inserty. But this is also probably Japanese storywriters at work – when they have the pen, Japan tends to carry the day, and given the setting, I guess I can't begrudge them awarding MVP to the home team.
I can't speak for the English dub, but the Japanese dub is hidden in the special menu (As opposed to under the “audio” menu like everything else), and pretty spot-on – everyone sounds like you'd expect them to.
As another review points out, it's not a gritty, serious story, and it doesn't set out to put Batman through the emotional and moral wringer. It's very much here for a fun time, those exotic concept arts you see and say “Wouldn't it be cool if that was animated” made so.
One for the enthusiasts, and those who are looking for a fresh take on Batman. If you liked the look of Batman: Shanghai and wanted more, this might scratch that itch.