Todd Phillips' follow-up to the most successful R-rated comedy of all time serves up its share of laughs while not actually providing a terribly enjoyable time because of a queasy undercurrent that never goes away. The pairing of live-wire Robert Downey Jr. with the slow-burning Zach Galifianakis strikes enough wild sparks to make this unendearing road trip a potent, if not sensational, late-fall commercial comedy for Warner Bros.