The story begins with Batman (Will Arnett) once again capturing the Joker (Zach Galifianakis). But all the other well-known villains also show up, mostly in tiny roles. Batman inadvertently adopts naive sidekick Robin (Michael Cera). He also has to work with new police commissioner Barbara Gordon (Rosario Dawson) and his resourceful butler Alfred (Ralph Fiennes).
The plot has the Joker sent to a maximum security prison with all the worst villains in history, e.g. the shark from Jaws, the miscreants from Gremlins, Daleks from "Doctor Who", King Kong, Godzilla, the Eye of Sauron from Lord of the Rings, etc. Inevitably, the Joker organizes a breakout and his new gang is soon terrorizing Gotham City as well as Wayne Manor and the Bat Cave. Not to worry, though, a feel-good ending is in the works. And despite all the action, nobody ever gets hurt.
How others will see it. At imdb.com, The Lego Movie has 330K user votes and a user rating of 7.7 out of 10. The Lego Batman Movie has 135K user votes and a user rating of 7.3. The Lego Movie had an Oscar nomination (Best Song), won three BAFTA awards, and won Best Original Screenplay (!) at the National Board of Review. The Batman Lego Movie also had many awards and nominations, but they were less prestigious overall.
So, the sequel was less successful, though undeniably popular. The user votes decline with advancing age, from 7.6 under age 18 to 7.1 among those over age 45. But, again, still popular. The user reviews are dominated by praise, e.g. "It's not just a great kids movie, it's a great Batman movie!!!" But of course there are also many complainers, e.g. "Totally lacks the fun of the first lego movie." Wasn't it Abraham Lincoln who said that you can't please everyone all the time? Something like that.
How I felt about it. Certainly, the movie has too many characters, even though some of them are strictly meant to be jokes (Condiment Man?). The plot is difficult to follow, since events move along briskly. The animation is good and the action is entertaining, but there endless eye candy for the kids, which can be overwhelming for adults.
Cultural references abound. To get all the jokes, you will have to have seen all of the Batman movies, in addition to all of the numerous films that source the worst villains in history.
But you don't have to get every joke to enjoy a "Simpsons" episode. You only have to get enough jokes for the film to be funny. And it often is. Because it's both a satire and a cartoon, it can go places that the live action Batman films can only dream of. Not just in terms of action, but character. Batman and the Joker can debate whether they have a relationship, Commissioner Gordon and Batman can argue whether the latter is a rogue vigilante or downsized to a partner.
Most Batman movies (e.g. The Dark Knight) take themselves too seriously. The character has an identity crisis. Is Batman amusement for kids and an in-joke for adults? Or is Batman a gloomy antihero essential for saving the world from permanent evil? My vote is for the former. It is true that Batman (1966) was too silly. But here, the mix is mostly right.