There were flood and it was just a halo version of like Left 4 Dead? The flood wouldn't be able to use any kind of weapons but their arms and there wouldn't be safe rooms. You would have to investigate what happened to the city (Why it's abandoned) during a flood outbreak. Would you have preferred this instead of what ODST really was? I really wouldn't have cared which way ODST went, it was good for me. These are just thoughts and if the community would have enjoyed this more.