Games are hard to make and, often, don't always get released with their original vision intact. From a gameplay pivot here, to a character swap there, most go through some pretty big changes throughout their development. But then there are some games that change course completely.
BioShock originally began life as a very ambitious game about a cult deprogrammer, with an asymmetrical multiplayer mode that would see you play as a monster in another player's story mode. Assassin's Creed was originally a follow up to Prince of Persia: The Sands Of Time, and its name used to be Prince of Persia: Assassins, before the Prince was dropped completely.
There are countless more examples, and the video above explores 7 games that were something else entirely.