This movie feels like a standard road trip story, but it’s populated by characters who consistently make poor decisions, leading to an unsurprising storyline full of expected jokes. Galifianakis delivers a portrayal that comes across as even less amusing and dumber than his role in 'The Hangover', while Downey's performance is a shadow of the wit and intelligence we see from Tony Stark. Frankly, this film isn’t worth investing your time in. If you’re looking for a comedic road trip movie, it would be far better to watch ‘Planes, Trains and Automobiles’ again. It doesn't matter how many times you've already seen that one; you'll likely feel much more satisfied than if you had spent the time watching this film instead.

Source on TMDB