Rafe's story is being told by a middle school narrator and is aimed at a middle school audience, so it's pretty easy to understand…both language-wise and if you've even had to suffer the indignities of middle school yourself.
Plus, it's also funny, insightful, and just plain enjoyable to read—that's always a huge plus.
Double-plus/pro-tip: the book is packed with illustrations. As you're reading, take the time to stop and enjoy the artwork. Rafe and Leo pack a whole lot of detail into those drawings, and you won't regret a closer look.