Sibling rivalry is the ultimate theme of “The Lego Movie 2: The Second Part,” so it’s not unreasonable to compare it to its own screen relatives. The direct predecessor of 2014 was a pleasant surprise, and its spinoff “The Lego Batman Movie” and distant cousin “The Lego Ninjago Movie” were moderately amusing. The newest addition to the toy-based clan turns out to be the least of the lot, an incessantly busy, jokey but charmless concoction that squanders the good will engendered by the previous installments.

“The Second Part” is set a half-decade or so after the first, which ended with a rapprochement of sorts between young Finn (Jadon Sand) and his father (Will Ferrell) about how to enjoy playing with Legos, the opposition of the kid’s imaginative approach to the older guy’s adherence to a rulebook mirrored in the conflict between ever-happy builder drone Emmet Brickowski (voiced by Chris Pratt) and President Business (Ferrell), who intended to freeze the Lego world permanently.

Now Bricksburg is threatened anew by surrealistically assembled, babbling critters constructed by Finn’s younger sister Bianca (Brooklynn Prince). Eventually the whole city is reduced to a mass of rubble called Apocalypseburg by these space invaders, and although Emmet retains his Candide-like enthusiasm, building a little house in the desert for eventual connubial bliss, his girlfriend Lucy (Elizabeth Banks) has morphed into a fighting machine called Wyldstyle, intent on protecting what’s left.

A further attack from the skies is led by a helmeted warrior called Sweet Mayhem (Stephanie Beatriz), who kidnaps Lucy, Benny (Charlie Day), Princess Unkitty (Alison Brie) and Metalbeard (Nick Offerman), as well as Batman (Will Arnett), and takes them to the Syster System, where shape-changing Queen Watevra Wa-Nabi (Tiffany Haddish) intends marrying the one she calls Man-Bat. A bunch of hand-picked heroes sail out to rescue them, but never return.

So Emmet springs into action, constructing a spaceship for himself. But he succeeds in reaching his destination only because of the intervention of Rex Dangervest (Pratt again), a daredevil archaeologist in a ship with a dinosaur crew who becomes Emmet’s mentor in derring-do. Emmet finds that almost all his friends have been seduced by the Syster System’s pop music—Batman even succumbs to the queen’s manipulation of his need for validation—except for Lucy. The two work feverishly to break the spell controlling their comrades and derail the wedding of the queen and Batman, though in the end it’s revealed that things—and characters—are not at all as they seem.

All of this is tied in with the irritation the kids’ mother (Maya Rudolph) is feeling over their constant bickering, and the threat of what Emmet calls “Our-mom-egeddon,” the very real possibility that unless they stop and learn to play together nicely, she’ll make them put away their toys entirely.

“The Second Part” is certainly crammed to overflowing with jokes, pop culture references, snide asides, goofy non-sequiturs, and hectic action, not to mention the cascade of gaudy animation, live-action sentimental montages and oh-so-clever musical numbers (one of which is simply titled “Catchy Song”—you know, the one that’s designed to stick in your brain whether you want it to or not, though in this case it’s not all that memorable). There’s an abundance of stuff constantly happening here, so much that you might be inclined not to notice that individually most of the bits are not all that engaging. As it piles incident on incident and moves into a final act involving a weird shift into perspectives altered by time travel, the movie has become more like an assault on the senses than a pleasurable jaunt into adolescent rivalries.

That’s not to say that “The Second Part” doesn’t have its funny moments, of course—including the final song over the closing credits—but far fewer than in the previous installment, and the heart-tugging is much less resonant this time around. In all, like the recent “Ralph Breaks the Internet,” this is an animated sequel that doesn’t live up to the original.