I don't have much to say about this book that won't spoil things, so I'll keep this short.
In Requiem, the story alternates between Hana's POV and Lena's POV, which is an interesting format. There's not quite as much action as there was in Pandemonium, but I enjoyed getting into Hana's head and seeing how the procedure affected her.
Throughout the book, there were a few scenes I disliked and wish they would have gone differently. For the most part, though, it was an entertaining story. I was really enjoying myself up until I realized I was almost done with the book and I thought, "That's not possible; there's too much left to resolve!" Well, none of it gets resolved. Not one single thing. I don't want to say more and spoil the ending, but I'm not kidding. So, if you haven't started the series yet, keep in mind that you'll never find out what happens to these characters. If that will disappoint you, then I cannot recommend the Delirium Triology.