The third (and seemingly final) Night at the Museum movie takes Ben Stiller's night guard Larry Daley to London's British Museum, where he and his exhibit cohorts attempt to solve a mystery that threatens the magic that began in the first film. Featuring a cavalcade of special effects and a handful of new characters, the weirdly subtitled Secret of the Tomb is about as enjoyable as the first two movies -- that is, for families and younger audiences, it's not the worst way to spend a holiday afternoon. However, also like the first two, Night at the Museum 3 won't be making anyone's "Best of the Year" list, despite its all-star cast and Disney-like charm.Eight years running, Fox's modern fantasy franchise is starting to show its age, as are the returning cast and crew. Stiller's deadpan humor is ever present in this third installment, but that could easily be mistaken for the actor's growing lack of enthusiasm. Stiller also plays a neanderthal that looks strikingly like his main character Larry, but the less said about that the better. Costars Robin Williams (Teddy Roosevelt), Owen Wilson (Jedediah) and Steve Coogan (Octavius) seem to be having a bit more fun than Stiller, but only just. In fact, the most enthusiastic returner here is Dexter the capuchin monkey, whose half-practical, half-CG performance will probably get the biggest rise out of young viewers.That said, the simple story moves at a brisk pace, and there's plenty of madcap chase scenes and comical set-pieces to keep kids and their parents engaged. Director Shawn Levy is also back for this one, and he does a fine job of maintaining the eccentric but consistent style of the first two Museum pics. Screenwriters David Guion and Michael Handelman (Dinner for Schmucks) pick up the father/son dynamic established in the earlier films, only here Larry's son Nicky (now played by Skyler Gisondo) has decided he wants to DJ abroad rather than go to college. This subplot is easily the most strained and lifeless, and lacks the heart the characters put into it in the first Night at the Museum. Luckily, that storyline takes a backseat to the nighttime magic and mayhem.As for the new characters, Rebel Wilson plays Larry's British counterpart, a sassy museum night guard that feels like a PG version of her lewd, crude Fat Amy character in Pitch Perfect. Downton Abbey's Dan Stevens suits up as Sir Lancelot, a dashing, Monty Python-esque rogue. Honestly, his character loses steam a few minutes after he first shows up, although he does bring about one well-timed cameo from a popular superhero star. Meanwhile, Sir Ben Kingsley pops up as a privileged pharaoh, and does more in his five minutes of screen time than anyone else. (He has some especially great banter with Stiller over the biblical Exodus -- funny, given Kingsley's recent turn in Exodus: Gods and Kings.)In terms of comedy, Secret of the Tomb is squarely aimed at children, so it's hard to qualify its sense of humor. There are a couple jokes thrown in for the older set, but rarely does it hit that sweet spot of entertaining all ages at once. Thankfully, its colorful and zany visuals carry it through to the end, regardless of the talent's vigor. Strangely, there are also moments where the movie goes for Pixar-level poignancy, but it almost consistently fails. The one exception is Robin Williams' final scene -- this is one of his last performances -- which is sure to put a lump in your throat, if only by virtue of the actor's recent passing. However, much like the rest of those tender moments, it doesn't quite feel earned, even with a pair of forebears under its belt.