• The team wanted to call the Locusts "Geist" but didn't since Nintendo has a game with the same name.
• They at first designed a first-person shooter (FPS) without cover, but changed into a sort of "Resident Killswitch" type of game design based on Resident Evil and Killswitch.
• Some of the ideas that did not make it to the game: "Combat Cash" that allows players to loot and get cash and "Morale Meter" that allows players to commit suicide when they're depressed.
• The ideas the team stuck to in designing are: slower paced game, no aliens from space, low tech and high tech and embracing cliches and shedding others.
• Camera inspiration came from Resident Evil 4.
• They decided to go with a toggle cover system instead of using the left stick to cover because the latter can get pretty annoying.
• The Y button was originally unassigned, but the team decided to turn it into the cool button. Thus, it was born.
  

Via Kotaku