X-Com Enforcer wasn't the planned 3-D shooter. X-Com Enforcer was apparently an action game that had you wandering around during the time period of the first game shooting aliens and collecting power-ups. IIRC, it was an action game, but not fps.
The fps was supposed to be a squad-based game (i.e. you had squadmates backing you up and responding to orders) that involves a team of X-Com squaddies that return to Cydonia to investigate some odd signals, and find themselves and their starship transported into the middle of a battle between the old X-Com baddies and an entirely new race of aliens.
Incidentally, X-Com Interceptor had some news reports that were meant to tie in to the fps indirectly. The reports involved humans (not in the game, though) discovering the trail of the starship and following the trail for a short distance, but not being able to locate the starship itself.
There were some in-game films floating around on the net, but the actual game was never released.
Anyone else play e-mail X-Com when that was available?