While we have the pleasure of meeting a few aliens face-to-face, The Others as a species remain shrouded in mystery throughout the novel. (That's part of what makes them so scary.) We don't really know what their deal is, apart from the fact that they're bound and determined to destroy the human race.
They seem to be willing to go to great lengths to make it happen, too. In this book, for instance, they're gathering up human children who survived the attacks. It's not because they believe the children are our future. They're just tricking the children into killing their fellow humans. At the very least, then, we know they're sadistic.
Or at least some of them are. Our alien intel (which comes from Evan, who's an alien himself) suggests that there are more "good" aliens like him, though we don't meet any in this novel. He says:
"There were some of us who didn't think annihilation was the answer. I was one of them, Cassie. My side lost the argument." (71.46)
One last fun fact that Evan shares is that the Others are "pure consciousness" (71.87) who "haven't had bodies in tens of thousands of years" (71.85). What's more interesting is what he doesn't choose to share. Before he meets Cassie, he references how human extinction is "his people's last, desperate gamble" (31.29).
Is it just possible the Others are more vulnerable than we think? Food for thought.