End of Days, Fallen #3 by Thomas E. Sniegoski

Aaron and the other Nephilim are up against their biggest foe yet. The Angel of Destruction. Verchiel has been defeated but has a back up plan. One that will destroy the world.

I love how the series takes this turn into the Angel of Destruction. It's something that is bigger than the Nephilim. A safeguard in case the world takes a turn for the worst. Aaron desperately tries to save the world and keep the last of the Nephilim safe. They battle monsters, the second wave of the powers, and his own self in order to save the world.