Wait, you can't buy the expansion without buying the main game again? Bwah. No thanks.
Not that I care, anyway, as I got really, really tired of running from cover to cover for 15 minutes until I could find an alien, crashed ship maps that were basically all the same, and having a base that was pretty much finished well before I got to the end.
I didn't even finish XCOM, despite really enjoying the first half of the game. I just kind of ... stopped playing it. They can keep this.