Very enjoyable, and there were moments that had me crying from laughter. I'm very excited to see where Riordan goes from here, and I think he's improved as a writer from the very first Percy book.
The funny moments that really stood out to me:
The nametag; WELCOME TO CANADA; Mars's Prophecy.
There were quite a few others, but those were my favorites.
On another subject, I really appreciate what Riordan is trying to do with these books. The first Percy books, he tackled kids with ADHD and dyslexia, basically tried to tell them that they were still normal and that life could still be great with all of those problems. Here he's diversifying. Sure the two books in The Heroes of Olympus seem to revolve around two white boys, Percy and Jason, but there is such diversity in the cast. And those kids do heroic things and are just as intregal to the plot as both Percy and Jason. The cast of these books reflects the poplulation of current high schools better then just about any other YA or mid-grade book I've read. I adored Hazel and Frank. They were funny and brave. I'm very excited for the next book as I think we'll get more of them as well as the other characters introduced in The Lost Hero.
Another theme I'm really enjoying in these books is the sibling thing. How they're important, but not always what you expect.