I have loved the books in the Horrible Harry series since I was a kid. Now I get to read them to my kids, and they love them just as much.
Harry isn't a horrible person; he seems to like things that are more gross than horrible. He's mischievous, but I don't think that makes a person horrible either.
He's also a smart kid. He learned something (that was in a different book), and he used what he remembered to crack the code for a surprise the lunch lady created for some fun. I think he was a pretty good detective if I do say so myself.
Mary was slightly annoying, as she always is, and I think it's nice that Harry had a chance to put her in her place. I don't know why she had to ruin the whole thing about how he figured out the sequence. Maybe she was just jealous because he wouldn't tell her.
But I do like what Doug said. He said that Harry didn't need to use the information that he acquired for his gain since figuring out the whole thing made him feel like a winner.
Love it.