Killed Tiberium, the planned squad-based FPS. There was so little leadership that it was hard to determine how the game was exactly supposed to be played. Oh, and it was expected to be completed in eleven months.
Tiberian Twilight was originally planned for the Asian (read Korean) gaming market without a singleplayer, but was adapted into the conclusion of the Tiberium saga in order to increase sales, and to help make up for the economic failure of Red Alert 3 (which resulted at least in part from the game's DRM).
Franchise Killer: Tiberian Twilight may very well be the death knell for the Tiberian Series, having ended on a massive cliffhanger that fails to address many of the questions throughout the series. It in turn may have killed the Command and Conquer series entirely.
What Could Have Been: Tiberium would have featured a new generation of Titan walkers, a modular weapon called the GD-10 that could fire rockets, grenades, railgun rounds, or ion blasts, and would have been in 2058 Italy during the second Scrin invasion.