Storywise it is generic. Anything I call bland in it is the story and the characters. Both are bland. Exceptionally generic in the sci-fi mold. There is no depth to either but it's a FPS. A FPS being good does not rely on it's story or characters. I think Call of Duty and Battlefield are both great FPS's. Neither have more than the barest baseline of character or story. They would need filling out to make a Die Hard movie script.
Unreal Tournament was one of the best FPS's of all time - that Halo modeled many of it's features after - and it wasn't because of it's story and depth of character. Gears of War is the exact same thing. It is what is. The story in an FPS is the video game world's equivalent of a Michael Bay movie. It's there to get you from explosion to explosion. Nothing more.
That is not dead which can eternal lie and withs strange aeons even death may die.