Part of the problem is that the films have been essentially one-joke efforts, the joke being that, at night, the exhibitions at New York's Museum of Natural History and Washington's Smithsonian come to life, via special effects, posing various comic problems for security guard Larry, played by Ben Stiller. Sir Lancelot (Dan Stevens), who has a pretty good running gag of imitating Stiller's facial expressions, and Rebel Wilson as a zany security guard. On the level of shtick and spectacle, younger audience members will be entertained by the antics of the cowboy-centurion buddy team, and CGI fans will savor such effects as a three-handed battle scene set inside an M.C.