I can see why these books are fairly popular with a certain kind of preteen/teenager. The character is the sort of sarcastic unpopular kid you want to root for, there's some humor, and there's some pretty exciting action at the end.
Having said that, this book was not written well, and the entire thing was fairly obvious. I think that there have now been enough books written to know that when you're going to reveal the entire secret back story in the diary of someone dead, you're going to be writing a fairly boring book. You could just write the diary, post it on the internet, and call it a day.