Sequels are tough! Especially with musicals. Hollywood, Broadway, either way. “Grease 2,” “Love Never Dies” (the “Phantom of the Opera” add-on), the epically lousy 16-performance flop “Best Little Whorehouse Goes Public,” the unlamented “Bring Back Birdie” — tough, tough, tough, tough.

The good-enough success of “Frozen 2,” then, deserves medium thanks and your allotted Disney money. The story pulls Elsa the Snow Queen and her less magical but nonetheless charismatic younger sister, Anna, into a murky web of Shakespearean political intrigue, with a large dose of Scandinavian pagan mythology; late-’80s/early-’90s-style power ballads from songwriters Kristen Anderson-Lopez and Robert Lopez; and just enough Olaf (snowman) and Sven (reindeer) to please younger viewers who, for years, after the first “Frozen” conquered the world in 2013, went to bed and then woke up signing “Let It Go.”

In one surefire comic interlude, at top speed Olaf recaps the narrative events of the first “Frozen.” And the lightning-quick “Let It Go” reference proves that the Lopez duo hasn’t lost its comic instinct.

That said, “Frozen 2” is more of a hairy quest deal, and knottier emotionally than the first. All’s well in the kingdom of Arendelle long enough for a generic happy-townsfolk number.

Then Elsa (voiced and belted by Idina Menzel) starts hearing a siren-song female vocalist emanating from somewhere up north, beckoning, waiting to reveal the truth behind her magical snow-sculpture powers, and the sisters’ parents’ death by shipwreck (another Shakespearean flourish).

With Anna (Kristen Bell), Anna’s amiable, supportive boyfriend Kristoff (Jonathan Groff) and Olaf (Josh Gad) in tow, Elsa discovers a mist-shrouded land and a new set of human characters. One of many intriguing notions in “Frozen 2” deals with the memory properties of water, so that water, in various forms, manifests a series of visual clues to the sisters’ fraught childhood. It’s like Emily in “Our Town” revisiting her past, if Emily had ever learned to sing “Let It Go” in her more repressive era.

The moral here is clear and repeated frequently: Always do “the next right thing.” That includes letting a couple of Disney princesses wear pants when they trek to lands unknown. The Lopez songs do the job without unearthing another enough-already earworm on the order of “Let It Go.” But one of those is probably enough.

Since Kristoff didn’t get to sing much in “Frozen,” the lovelorn lunk treats himself this time to a wry music video of his own, delivering a power anthem titled “Lost in the Woods.” The movie itself occasionally gets lost in those woods, but finds its way back out again.