I would like to see X-Com: UFO Defense and Terror of the Deep both remade, hell, it doesn't even need 3D graphics, although those would't hurt. More complex country infiltration (say, being attacked by a nation's military if you have a base in the territory of a infiltratred nation), smarter way, even better destructible terrain, bigger maps, no more 80 itens limit, new alien foes, called shots at body parts, proper incendiary damage, aliens atempts to deny you tech, etecetera...
A TFTD remake would be very interesting if they did more research about the ocean. A "depth" diference in the map would be very interesting. Imagine sending a team of troops to the abissal regions of the deep oceans - It would be like UFO Defense's night missions, but ten times worse (for those that don't know, its FUCKING DARK 200 meters and beyond in depth). And also some things in a wish list for TFTD:
* Airborne Interception - what's the point of flying subs without air to-air weapons anyway?(Avalanches anyone?) Surely it's better to 'splash' the USO before it makes it to the safety of water?
* Alternatively, get rid of the pretense that subs can fly. How does sonar track a USO over land, anyway?
* Combined land/sea game, with subs and aircraft, USOs and UFOs, Aquanauts and Soldiers, land and sea bases. Now that would be cool!
* A slightly less dramatic change: on any land mission, automatically swap Dart Guns, Jet Harpoons, HydroJet Cannons and Torpedo Launchers for (respectively) Pistols, Rifles, AutoCannon and Rocket Launchers "from stores" (including their ammo of course). Purchase price of the weapons would be doubled (or just add the cost of the XCOM-EU equivalent) to reflect this versatility.
Essentially the game would switch icons and elements of OBJECT.DAT for a land mission. Could also switch Grenade types perhaps? But it's best to keep some underwater weapons (eg Gas Cannon), especially for land missions where there is some water present. Conceivably, in recognition of the progress made by XCOM, and the increasing threat, the authorities might even make available some of the scarce (?) stocks of laser weapons, to exchange for Gauss weapons during land missions. (But this is not really necessary, as Gauss weapons are quite adequate on land.) Working plasma weapons of course have long since vanished due to lack of Elerium. (Although by the same argument, 1st Alien War-era Personal Armour should be issued to any unarmoured troops on land missions. Maybe it takes 200% damage from Sonic weapons.)