Given that it’s a sequel/spinoff built around a mostly throwaway gag in The LEGO Movie, The LEGO Batman Movie is funnier than you might think it has any right to be. But those of us who were expecting something more can’t help but feel a twinge of disappointment. The LEGO Movie was a political-religious conversation in the guise of a very funny kids’ flick. In Christopher Miller and Phil Lord’s 2014 masterpiece, LEGO Batman was the brooding, narcissistic superhero boyfriend of the beautiful rebel fighter with whom that film’s Everyman protagonist was smitten. Obsessed with his own fashionable despair, LEGO Batman was a one-joke sidekick in an animated film that was otherwise boundless in its irreverence, creativity and metaphysical ambition. Can such a character sustain an entire film on his own?

He can, so long as you set expectations to “chuckle-worthy” instead of “sublime.” To be fair, director Chris McKay and his writers do find some variation within that one joke. (The screenplay is credited to “Seth Grahame-Smith and Chris McKenna & Erik Sommers and Jared Stern & John Whittington, story by Seth-Grahame Smith, based on LEGO Construction Toys and based on characters from DC,” and you’d better believe that every ampersand and comma and “and” of that was negotiated by a small army of well-paid lawyers.) They build on the idea of LEGO Batman (voiced again by the excellent Will Arnett) as an impressionably dour and lonely guy who has rejected anything that might resemble a friend or family, all in the service of his impeccably micromanaged gloom.

That means that when he’s not fighting LEGO bad guys or being lectured by LEGO Alfred (voiced by Ralph Fiennes), LEGO Batman has little to do except sit around his giant LEGO Batcave fiddling with the LEGO TV in his LEGO theater watching rom-coms and chowing down on LEGO lobster thermidor, quietly dabbing his LEGO mouth with LEGO napkins in the vast LEGO silence of his LEGO loneliness. That starts to change when Gotham’s longtime Commissioner Gordon retires and is replaced by his beautiful LEGO daughter, Barbara (voiced by Rosario Dawson). Our hero is so enthralled by her that he doesn’t even notice himself casually and carelessly adopting a young LEGO orphan named Dick Grayson (Michael Cera), who will, of course, become LEGO Robin.

But the real specter of overt emotional attachment arrives in the guise of the Joker (Zach Galifianakis), who desperately wants this Dark Knight to commit to a meaningfully antagonistic relationship and declare him his No. 1 arch enemy. But Batman can’t bring himself to do it. “Batman doesn’t do ships, as in ‘relationships,’” he sternly tells the teary-eyed supervillain in his hilariously somber rasp of a voice. “There is no ‘us.’ I don’t need you. ... You mean nothing to me. No one does.” The film takes this idea a bit further than you might have expected it to, building an entire conspiracy out of the Joker’s wounded feelings — though understandably for a PG movie with all those behind-the-scenes ampersands, it never quite goes homoerotic.

That’s about it, storywise. There is some business with the Phantom Zone Projector, a device that can send anybody, good or bad, off to the interstellar dimension where Superman once imprisoned General Zod. Really, the movie is basically all about the Joker’s hurt feelings and Batman’s trust issues. Luckily, it’s all funny enough within those modest parameters. As you might have imagined, LEGO Batman gets his own preening songs: “Ladies, it’s OK if you stare/Cuz I’m a billionaire … Who can choke-hold a bear.”

There are also pale echoes of The LEGO Movie’s adorably patchwork cast of characters. There, the presence of figures as random as Gandalf, Michelangelo, the Statue of Liberty and the 2001 NBA All-Stars spoke to the cluttered, surreal eclecticism to be found in any LEGO collection of some breadth. This time it’s a little more generic and corporate-friendly: When Joker calls on villains such as King Kong, Agent Smith from The Matrix, Voldemort and Sauron (“He’s a 9,000-year-old evil with an eye for jewelry!”) you’ll probably laugh a little, but you might also notice that they’re all Time Warner properties.

The LEGO Movie was a big studio hit that did well with kids and adults alike, but it also poked real fun at itself: Its LEGO World was one of stultifying conformity, and the fact that everybody ate the same food, did the same jobs and lived in the same spaces warned against the repetitive monotony of a prefab plastic reality. The film was good-natured, but its humor was so self-aware that you got the sense that any joke was possible, that nothing was off-limits — and its nonstop critique of all the common tropes of blockbuster movies seemed like an arrow aimed directly at its own corporate heart.

LEGO Batman has some of that same spirit, but it never goes far enough. Early on, someone suggests that Batman enlist a group of imprisoned villains in the fight against the Joker, to which he replies, “What am I going to do, get a bunch of bad guys to fight bad guys? That’s stupid.” Yes, it’s the mildest of digs at Suicide Squad, Warner/DC’s notoriously loathed superhero hit from last year. But guess what Batman winds up doing late in the film? It all feels so predictable … so conformist. The LEGO Batman Movie is entertaining, but it also sometimes feels less like a spin-off of The LEGO Movie and more like one of its targets.