If I had never seen a trailer for this movie, I'm sure I would have liked it a lot better. But unfortunately there were two different trailers, and they were played in front of every movie I saw over the last few months. Not to mention the TV spots that played on Comedy Central all the time. Most of the funny parts were in the trailers.
The story is pretty simple. Robert Downey Jr. is an architect and he is in Atlanta for work. His wife is in LA and she is going to give birth to their first child in a week. He is flying home to be with her, and gets kicked off the plane. He left his wallet on the plane, so he can't rent a car. He is on the no fly list, so he can't fly.
Luckily he met a really strange guy played by Zach Galafinakis (who is the reason he got kicked off the plane in the first place). He rents a car and offers to drive him to LA. It's hard not to compare this to Planes, Trains, and Automobiles. You have a normal guy and a buffoon as his traveling companion.
We wouldn't have much of a movie if they got to LA with no trouble. Galafinakis is an idiot, so he doesn't realize that renting the car will max out his credit card, and he doesn't consider the consequences when he spends all his cash on pot. Downey's wife wires them some money, but she has to put it in the other guy's name (since Downey's ID is on the plane), and Galifanakis forgets that the last name he gives is just his stage name, but his real last name is on his ID.
It's hard to write a movie like this and keep it realistic. There are a bunch of solutions that never occur to Downey because we wouldn't have a movie. His wife could wire him money - I'm pretty sure Western Union has an option where if the recipient doesn't have ID, they can ask several test questions to verify his identity. He could take a bus or a train, but this is never discussed. The movie spans 5 days, and the first day, the plane should have landed in LA. Someone in LA could pick up his stuff and fly out to where he is. We learn late in the movie that his wallet isn't actually on the plane, but until he learns this, he could consider the idea.
A few other things that bugged me: Downey is supposed to be a smart guy, but as soon as he is kicked off the plane, we see him trying to steal a rental car? Really? He actually thinks he can steal a rental car from the airport and just drive it home? He shouldn't be that desperate yet, but we don't see him consider any other options or ask anyone for help. There is a scene where they drive off a freeway overpass. Everyone in the car would be killed, but of course they only have minor injuries. And Galafinakis's character is just too stupid. Anyone as dumb as he is would never be let out. They tried so hard to make his character crazy that they made him a cartoon character. In Planes, Trains, and Automobiles, John Candy made his character an annoying buffoon, but he also was a real character that we felt empathy for. Not so much in this case.