I forgot Laser Squad Nemesis and Frozen Synapse. They have simultaneous turns, and in some ways it's the best of both worlds. You get the ability to plan moves carefully, like in TBS games, but don't get the time artifacts associated with them. Like in RTS games, time flows naturally. Try to distinguish between a shotgun and an automatic rifle in a TBS game. Good luck with that. The same thing is very easy in a game like LSN.
I like to compare simultaneous turns to crossbows. Both inventions were very good and have their merits, but (in western world) they came too late to matter.
Also, Laser Squad Nemesis is a game designed by original X-COM's designer. It's from 2003, so and has nice high-res 2D graphics.
It has very nice mechanics. I especially like the unlimited shots of opportunity fire (well, limited by the ammo left in the clip) that allow for fun play while being hugely outnumbered.
It looks promising so far. The game actually explains mechanics to me is a good sign, it reminds me of Debian. Another interesting thing is separate action and movement points. I've been thinking about something like that. Basically the idea is you can move your legs separately from your hands.
+1 for LSN: back in '04 a friend of mine and I must have spent at least 50 hours playing nothing but the hotseat multiplayer of that game.
FS is also a lot of fun, but it just isn't as deep or complex as LSN. Fewer enemy types, less variety in level design. On the flip side, though, this means that most matches are over much quicker than LSN (a one-sided match often took 20-30 minutes, and hotseat games back in the day often took us an hour to finish!)
Crossbow too late to matter (you said "in the West", and my comments are likewise restricted), though... whatchu talkin' 'bout? Crossbows in Europe are over 2000 years old, so "too late" seems a little improbable. And they were the dominant ranged weapon in most of Europe for hundreds of years (roughly 1100-1500), so they totally mattered.
Laser Squad Nemesis is a great game. I remember spending too many hours learning and trying to properly implement the lessons of The Grenadier’s Bible.
Also, Laser Squad Nemesis is a game designed by original X-COM's designer. It's from 2003, so and has nice high-res 2D graphics.