JMayer70: I know, you mean that Terror From the Deep, not had the pleasure of it yet, is it really that bad?
Schwertz: No. It's not bad of a game since actual gameplay is improved version of UFO: EU. May be over-hardened, though.
But it is definitely a bad X-Com. Because lore, visual style and certain lack of basic logic make it some sort of lovecraftish total conversion. Microprose of UK wanted a quick sequel after the success of Enemy Unknown. And they considered expected terms of development of Apocalypse unsatisfactory. So, while Myphos games were busy with the real sequel, Microprose's management gave the task to do something quick to the own internal studio. This way we got The TFTD. Turned inside-out Enemy Unknown with replaced graphics, submarines which can fly, aquanauts which can not swim, Zrbite instead of Elerium and other clumsy replacements.
Old post, I know... but I had to defend TFTD.
In "my" personal opinion, the only X-COM games worthwhile is UFO: Enemy Unknown, Terror from the Deep, and the newer ones. There was a whole slew of X-COM games that came out in between those originals from the early 90s, and I really didn't find any of them to be any good. But TFTD was a fantastic game, and I enjoyed every bit of it.
These games... the Afterdark, Afterlight, Aftershock (totally out of order, I know) were also spectacular. In my opinion, I played these A/A/A games as a spiritual successor to pacify me in between UFO/TFTD, and the newest ones. I really wouldn't bother with the others. They are probably good games on their own, but really somewhat unrelated and just using the name.