The Sea of Monsters, second book in Rick Riordan's Percy Jackson series, seemed to be an even better story than the first. Maybe this is because the whole "world" of the Olympians, Half-bloods, and all their mythical monsters has already been established and the reader already knows the characters. At any rate, I didn't feel like I had to take time suspending my disbelief at the whole enterprise...; I felt like I was able to start right in and accepted this world for what it is. 
 I also was able to get a stronger sense of where the storyline for the series was going. This isn't just a one-book "boy-learns-he's-son-of-the gods- and comes-to-terms-with-himself- during-great-quest". We see now the conflict with Kronos' attempt to regain power and destroy civilization as we know it. Additionally, this book helps to further develop the characters met in the first book. I find that there is some really nice character development in this series, and the reader comes to appreciate and care about the characters. 
 This series is extremely popular with the 3rd, 4th, and 5th graders I teach. It's easy to appreciate the action and humor, but I'm also glad for the exposure the series gives to mythology and well-developed characters.