Should have...

They should have, or perhaps for a future game make it an online open world game. Just imagine, you run around as your created character, meet people or groups and do missions together or just run around freely blowing up machines. you can leave team anytime you want and explore solo where you hear coming from your headset another player yelling for help as he's pinned down, and run over to assist. Just things like that, where you meet up with ppl and discuss strategy and what not how to kill the machines, and do minor missions together. etcc...that would have been awsome! Who knows maybe if a game developer reads this, they can make it.