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If you dig Sci-Fi combined with philosophy, i'd suggest Bernard Weber's The Empire of Angels, it is part of a cycle : Cycle of Angels, preceded by the book The Thanatonautes.
I love his books to bits.
Hush, Hush series by Becca Fitzpatrick or Angelfall by Susan Ee is good too. I prefer the latter though. There is a movie adaptation of the book Fallen by Lauren Kate if you're interested but in my opinion that sucked. The book was okay but the film sucked bad.