One of the most original games I've ever played was the first Tribes for PC. If that game had a campaign it would have been much more popular, but in 1998, what you could do and how fun it was blew me away. First real MMOFPS where you had to use tactics and junk, vehicles that flew and shot rockets, and you used jetpacks to get from place to place. Teleporters, deployable walls and force fields, turrets... I don't think I've ever played a game more...