When I read Dark Moon, it was a bit difficult for me to get through; I cannot quite explain why, just that the story did not enthrall me as much as the previous one.
However, I did love the introduction of humans and the main characters are all enjoyable. I have never been annoyed with any of them, though that often is a problem for me, when reading.
The story is an important part of the trilogy and I recommend that people who loved the first book, read it, it shows the trio that we love as they mature and reach adulthood.