Grandma's Boy is funny and enjoyable. It's a dumb comedy that sticks to the core premise of dumb comedies: they can't be cynical.
Contrast this movie to Knocked Up and you'll see what I mean. Both movies have raunchy humor and a lot of f-bombs (though I'd say Knocked Up wins in both categories). They both rely on a random humor element, rather than the core plot being funny. However, Knocked Up has an undertone of bitterness and cynicism that makes it really unfunny and unenjoyable. Plus, Knocked Up is way too long, extending the pain if you cared to keep watching.
As a few of you know, my favorite comedy of the last few years is Harold and Kumar Go To White Castle. Other than that, I really haven't enjoyed many of the recent spat of comedies. 40 Year Old Virgin had a few moments of gold, but was otherwise overlong and forced. Wedding Crashers was another one of those movies with an undertone of bitterness. I did mostly like Old School and even liked some of You, Me and Depree.
Most comedies miss the mark when it comes to creating a classic like Caddyshack, Better Off Dead, or Animal House. Those comedies are what they are because they create funny characters and put them in environments that make them shine. Grandma's Boy is like that. I'm not saying it's a classic like those three I just mentioned, but it does have the same formula. It revolves around a 36 year old video game tester who moves in with his Grandma and her roommates. Like Caddyshack, a few funny characters are focused on and the rest end up being role players in the hilarity.
I don't really want to give away more than that, it really is a must see. The co-worker who loaned it to me told me that it was really offensive. Compared to Knocked Up, this movie seemed tame, funnier, and more enjoyable. And... it's not overly long! Finally, someone made a movie in the 2000s that isn't too long!
JSS RATING: It's a Good-Bad Movie. Meaning it's in the traditional film critic category of "bad movie" but is really good.