Bioshock Infinite's ending was well...a little ambiguous. First we get the punch of just exactly who Booker and Elizabeth are. Then we're in Rapture. Then there's lighthouses everywhere...it was a all a bit too much in rapid succession and the latter parts didn't get explained too well. Just how many Universes are there? Is there more than one Rapture and Columbia? Do they exist in the same timeline? Any new developer needs to straighten the series' rules out. Now we don't have to go into Midichlorian levels of explanation, but something to let us know where we stand in the Universe would be helpful. it also opens up literally worlds of storytelling opportunities.