I saw the movie version of this a while ago and while I wasn't a huge fan of it, I've been wanting to give the book a try. I found a copy for a few bucks in the clearance section and read most of it in a day.
I can't stand Greg Heffley. He is one of the most irritating characters I have even encountered. Self-centered, selfish, and clueless, I really don't understand how this kid has even one friend. This is less of a diary of a wimpy kid and more of a diary of a total jerk. He never thinks of others, including his supposed "best friend". He makes fun of everybody and is overly focused on his popularity even though he hardly engages with any of his peers, besides writing about how stupid they are. Greg thinks he's better than everyone and isn't afraid to express it.
The worst part of the whole thing was that Greg learns nothing in the book. I'm a sucker for stories where flawed characters gain even a little insight into how horrible they are, but Greg is just too dense. Beginning to end, he is too focused on himself to even realize that other people have thoughts, emotions, and feeling.
I don't like overly sentimental books either, but this one had no depth at all. It's just a list of events that might be remotely humorous if I didn't hate the character so much.
A very quick read, but I did not enjoy it.