You know what? X-COM is like The Matrix. There were and still are no sequels. There were a few cash-ins and a couple of half-hearted attempts to remake the original, but really, there's UFO Defense/Enemy Unknown. Everything else either pales in comparison, sucks in comparison, sucks (full stop), or in the case of the latest game, is totally disconnected from X-COM in all but name.
It does say something about the original, though, that there's still developers and publishers trying to cash in on the name, nine years and however many bad follow-ons later.