Openxcom is all I need right now and I'm looking forward to modders doing the same for Terror of the Deep.
This. One of the few games I'm looking forward to playing again is a non-messed up version of TFTD. Many dismiss it as an inferior clone to X-COM, but if you just untangle some of the mess (like the bugs in the research trees) and you've got a game that outcreeps X-COM by miles, IMO.
Chryssalids are scary? Try having a flying version of it with even more TUs. I'd be even more scared of Lobstermen if I didn't know their one weakness and that the game sometimes locks up into having NOTHING but Lobstermen running around, so I'm a seasoned lobster cook by now.
Fun fact: There's a monster in TFTD that's so rare to encounter that most players don't even know it exists: The Xarquid. There's a Codexer posting these days that has it as his avatar, but I had played (and completed) the game at least twice before I could even retrieve a corpse of one, I've never had a chance at a live recovery in the 20 years the game has been out.