The end of the book provides some closure: Cassie and Ben have fulfilled their sacred mission of saving Sammy, the aliens' main military base has been blown to bits, and Cassie and the gang are headed off to relative safety.
Not too shabby.
Remember, though: The 5th Wave is the first book in a trilogy, so it has to leave us hanging. That's just how it works. So, for one thing, we don't know whether or not Evan survived the explosion. Also up in the air? What our heroes are going to do now that they've saved Sammy. Will they be on the run in Book Two? Will they find a way to fight back? Will humanity itself survive?
We can't say for sure, but the book's final image may provide a clue. "The three of us watch the sun break over the horizon, obliterating the dark in a burst of golden light," Cassie tells us (91.36).
That sounds pretty hopeful to us.