In this film, Robert Downey Junior plays a man who's baby is about to be born across the other side of the country and can't fly there so has to drive there with nutty Zach Galifinakis who's father has just died and who's a bit of a wierdo. Albeit a nice wierdo. It's a comedy with with RDJ playing a serious guy and ZG playing a more layed back, goofy guy.
It has it strengths and weaknesses. One of it strengths is the partnership of the two characters as they couldn't really be more different and they clash in a funny way, however the comedy is a bit too boring at times. Another strength is that it's quite a good length, just short of an hour and a half so it's not spaced out too much like some films can be.
One of it's weaknesses is the lack of female presence. Michelle Monaghan is briefly in it, playing RD Junior's gorgeous wife but she should be in it more, especially given how attractive she is. Also, the brief story of Downey's character thinking Jamie Foxx (his friend in the film) has pregnated his wife, rather than him, seems to just disappear too easily and more could and should have been made of this.
As I said before, the comedy is too boring and should be funnier more often than just 3 or 4 times during 90 minutes. For a comedy, it's not really funny enough. It only made me laugh out loud two or three times.
Overall however I'd say this is a 6.5/10 and worth a watch, dependant on your comedy taste.