I have finished this book some months ago, but only got around to reviewing now.
This is the last book in the series. I was saddened by this, because I had really grown to love the characters. I did like the ending though. However, I wouldn't mind short stories about them like five years down the road. Some story lines had a rather abrupt ending, I felt.
The story branched off in this book as well. I was very glad to see Nico have his own voice. He had been a favourite of mine for some time.
Overall, it's very hard to talk about this book without spoiling the others. I am glad that I read all five books together, because they came together as one more than the previous five. They were also more adult than the previous five. While both end in battle and some deaths, this was different. In fact, there were more than one battles, and all of them were unique. The talents of the different demigods were used in complex ways, and there wasn't just one individual that stood out.
Reading this series as someone completely out of the target demographic, as a 32-year-old woman, I still enjoyed it. It was fun on one hand, but the characters were complex and individual enough to make me care about them. Even though they were half my age, their struggles were very adult. I wondered if it really was for kids, and they are, but for the more mature. However, adults can also enjoy them, because the topics are very mature. What were those topics? Well, dear reader, you'll just have to find out for yourself. ;-)