Maybe if I was a fan of the game I'd like this better. Read it because my teenage son recommended it.
Defenders of Mankind is actually an omnibus of 2 novels and a couple related short stories.
The first novel is The Death of Antagonis by David Annandale. I didn't care for it and it was very hard for me to get into it.
The 2nd novel was Death of Integrity by Guy Haley. I enjoyed this story and accompanying short stories much more, but still 3.5 stars for me.
Generally speaking, it was hard for me to get into the back story and fantastical parts of world.