There are spoilers below, if anyone cares. No reason you should.

A guy who's a real loser gets a job as night watchman at a museum where the exhibits come alive every night.

And that's pretty much it. Good special effects, but it's Ben Stiller, so you can pretty much write the script yourself. They kept vacillating between whether the human figures in the exhibits were really themselves (i.e. had knowledge and skillsets of people of that time) or were just knowledgeable from hearing tour guides talk about them over and over and over.

Robin Williams, Owen Wilson and (what a waste) Steve Coogan are three of the exhibits (Teddy Roosevelt, a guy from the American West and a Roman general, respectively) and get to do some silly stuff, none of it very amusing. Dick Van Dyke, Bill Cobbs and the extremely creepy Mickey Rooney are the three outgoing security guards, and it's fun seeing Dick Van Dyke be evil. But not that much fun.

The ONLY THING in this whole movie that made me and Mr. Otter actually laugh and point at the screen in enjoyment was the tail-waggin' T-Rex skeleton who just wanted to chase bones. And even that got old.

Another movie that probably sounded good over a three-martini lunch, but failed in execution.