I am one of those people that normally hate Will Ferrell, especially in a leading role. I find him obnoxious, and over-the-top to the point where he is pandering for laughs form the LCD than actually attempting to be funny.
However, there is always an exception to the rule. Usually that exception comes in the form of a supporting role... as in Old School... but here it comes in the form of a leading role.
It seems like Marc Forster really reigned him in on the one and the pay off was AMAZING. It's seriously a funny and quirky film. It's hysterical and kind of plays to an audience that wonders if writer's creations can come to life.
It's an imaginative script and plays to the people that feel, maybe, a little guilty for leaving a book over night when the characters are left in a bad position just in case they are real and might get stuck there. It appeals to anyone that has ever wrote fiction, and felt like a God because of the control they had over their characters... and it does so in the most ridiculous way possible.