I've never played X-Com either, but this does sound kind of cool, so when I'll check it out as more info becomes available.
I do agree on this part, though. That fucking sucked. I wish it was more like Oblivion than it already was in that respect, looooong game, one biiiiig piece of DLC.
And yeah, I was able to get about 170 hours out of Fallout 3 from the base game, and then about 190-ish from the DLC, but with Oblivion I have a fair bit over 200 hours.