Another ostensibly-for-kids movie that Mrs. Salad and I thoroughly enjoyed. Part of the secret was revealed in the credits: based on a book by William Joyce. We used to read his wonderful books to the kids. A lot of his genius shines through here, in both the inventive animation and the storytelling.
The main protagonist is Jack Frost: his origin is mysterious, in the sense that he doesn't remember how he got to be Jack Frost at all. But he enjoys giving kids snow days and fun times in the frigid temperatures.
Still, something's missing. He's given a chance to find it when he is invited to go on an important mission with the good-guy Guardians: Santa, Sandman, the Tooth Fairy, and the Easter Bunny. Their nemesis is "Pitch Black", aka the Boogeyman. He has a nefarious plot to defang the Guardians by making the children of the world disbelieve in them. And henceforth the world shall be in the thrall of darkness, fear, and hatred.
It's fun to have a bad guy that's really bad.
It's full of beauty and humor. Plenty of sight gags in Santa's workshop.