Some roles follow actors around their entire careers - Anthony Perkins in 'Psycho', Linda Blair in 'The Exorcist', Howard the Duck in, well, 'Howard the Duck'. Within minutes of first appearing as befuddled man-child Alan in 'The Hangover', Zach Galifianakis had put a classic comedy performance on his CV. He made the movie, arguably deserved a Best Supporting Actor Oscar nomination for his work and left you wondering what his next big job would be.

The answer is a bit more of the same.

Directed by 'The Hangover's Todd Phillips, 'Due Date' is another story of a man in dire straits, trying to make it back home for one of life's big milestones, only to have another bearded misfit causing far more problems than he solves. It's a movie that proves that Downey Jr should do more comedies and that, for all his charm, Galifianakis should leave this kind of character behind after 'The Hangover' sequel.

Downey Jr plays Peter Highman, a control freak architect with anger issues whose impending fatherhood has only made him more uptight and obnoxious than usual. Leaving a business meeting in Atlanta, Peter's plan is to get home to Los Angeles in plenty of time for wife Sarah's (Monaghan) admission to hospital. Then he meets Ethan Tremblay (Galifianakis) at the airport and begins to learn quickly - and very painfully - that life doesn't care about your plans.

Within an hour of crossing paths with the aspiring actor, Peter has been accused of trying to bring drug paraphernalia through security, shot with a rubber bullet by an Air Marshall, thrown off his flight without his wallet and put on a 'no-fly' list. Thankfully, there's one good Samaritan willing to give him a lift all the way to LA. Trouble is he's the fool who has caused all the trouble in the first place.

'Due Date' wants to be held in the same esteem as the shrine-deserving buddy road movies 'Planes, Trains & Automobiles' and 'Midnight Run' but isn't as strong or memorable as either and relies too much on both for its dynamics. Here we find director Phillips trying to grow up a bit by including some heartfelt scenes in between the gross-out gags and examining how two men with nothing in common try to reach some kind of understanding of each other and their relationships with their fathers. They fight; they make-up, they fight again; they make up - and you feel that the film is rushed in places and too slow in others.

As the success story who defaults between brusque and downright nasty and the skinny jeans-wearing buffoon who sees the good in everyone and brings out the worst in most, Downey Jr and Galifianakis have plenty of chemistry - a good double act that could have been great. They make sure this movie is never a chore to watch, but aren't given enough to make it a must-see.

Harry Guerin