I really wanted to like Envy, it has everything going for it and while I did struggle a bit with the frequent change of POV in the narration, I enjoyed reading about Hayley and Taylor trying to unravel what had happened to Katelyn.
Envy is very detailed; when you add the masses of characters as well it's easy to get lost. Occasionally the writing comes across as very deliberate, creating `atmosphere' but not actually helping the story. I predicted some of the outcome, not all of it, and was quite happy to invest in the next book in the serious until I reached the last few chapters.
My problem with the ending isn't the resolution to Katelyn's mystery but relates to the subplot. The chapter on page 282 ends with "It had to be done". No it did not. There are many other ways this could have ended most of which would not have resulted in me completely losing all respect for the protagonists.