Hot dog! We have a wiener!
Identity is the big problem of why X-Com is very different than other games, and why people that see FPS start to nerd rage. Trying to make Fallout or Metroid comparisons is just invalid. In Fallout, *you* were the vault dweller (or chosen one). In Metroid, *you* were Samus. Yes, there were other characters that might have been involved, or even fought along with you, but the player's identity was well established. Changing perspectives was a big risk in both of those franchises, but they were always first person "story," regardless of how the actual gameplay was presented.
In X-Com, the player had no real on-screen identity. In theory, you were in command of the X-Com program, and you certainly issued orders for your troops in battle, but you were never identified as an actual person in game. *You* never stormed into that random South American farmhouse, your employees did. Nameless and silent, you guided an entire multi-national enterprise. Hell, if you wanted, you could imagine yourself as some kind of ambiguous "SEELE-esque" council of benefactors, guiding humanity from the shadows.
The very nature of first person will remove that ambiguity, forcing the player to adopt a specific identity. Even if they make you a silent everyman ala Gordon Freeman, the player's identity is set, and major change in tone will have been made.
It's not that I want the game to fail. In fact, X-Com is a universe rich in details that would make for an excellent squad based shooter (8 man co-op! with heavy plasma! and remote controlled tanks!), it could be a blast.
But being told I'm demoted to Mulder wannabe?