First off, I want to say that Zac Efron's acting was superb in this movie! I never liked him much ever since watching him in his previous movies, HSM and Hairspray) with his wooden acting, but he was excellent in this movie. He had the role down pat and modeled it after Matthew Perry's acting style, which remind me of Chandler (from "Friends").
The basis of the movie starts off with Mike (Perry) who is unhappy with his current situation and wishes that he could go back to his glory days. He sort of gets his wish, but not the in the way he expects it.
The setup of events are expertly placed, making the storyline flow smoothly and intelligently. For example, although Mike is his younger self, he still manages to interact with his wife and children and maintains the relationship throughout (you will understand what I mean when you watch it!)
While the majority of the movie focus' on Mike, the subplot with his best friend, Ned is hilarious, so look out for his moments.
There are definite LOL moments and very sweet/cute moments that make you go "awwww".