Due Date, director Todd Phillips’ follow-up to last year’s hit The Hangover, doesn’t offer much in the way of a premise: Soon-to-be-dad Peter (Robert Downey Jr.) misses his flight home and catches a ride with aspiring actor Ethan (Zach Galifianakis), and the mismatched pair embarks on a two-day road trip from Atlanta to Los Angeles. Like The Hangover, and Phillips’ other new-school comedy classic Old School, it all comes down to the actors at the center of it all. The Hangover made Galifianakis a star, and in Due Date he plays pretty much the same character – the super-annoying guy who means well, this time with a bad perm and pink Lilith Fair shirt. (He’s also misguided in his vocation: “Two and a Half Men is the reason I wanted to become an actor,” he tells Peter. “Especially the second season.”) The key to the movie is the interplay between Downey and Galifianakis, and they have an easy rapport. The characters they meet along the way – played by Jamie Foxx, Juliette Lewis, and Danny McBride -- add to the fun, but it’s the scenes the two stars play together that keep the otherwise generic story moving. Downey is especially good, showing more reserve than he did in his flashy (and overrated) turns in the Iron Man movies. Of course, Peter and Ethan learn something about themselves. But Due Date isn’t about the destination. It’s about the wild and funny trip.