8. More Weapon Abilities 
Believe it or not, weapons in Firaxis XCOM have special abilities. One of those abilities is Overwatch, firing rounds whenever an enemy moves within a soldiers line of site. Another is Suppression, the ability to lay down a barrage of fire to keep enemies from moving (and giving a chance to shoot them if they do move). And theres even an ability that prevents you from firing after youve moved. Where can you find these abilities? Deep in the configuration files for the game, which are easily accessible if you play the PC version. You can easily add the suppression ability to any gun in the game (although youre better off sticking with the rifles and machine guns), which adds a whole new layer of tactical depth to the game. Got a bunch of enemies and no high probability shots? Suppress them so you can move up in your next turn and take them out. Got an alien you want to capture, but no soldier with an Arc Thrower immediately close by? In the stock game, youd be screwed if you didnt have a properly specced Heavy or Support soldier to suppress them. But if youve got any soldier with a rifle, you can pin down that alien, as long as you dont mind eating up 2/3 of your soldiers ammo. So what new abilities could be added? One obvious option is some sort of grenade like attack, like Mass Effects concussive shot and carnage attacks. Another is a souped up version of Disabling Shot that could be upgraded to stun aliens with up to 3 health by using the Foundry. Who knows what else Firaxis could think up, especially if they radically alter the weapons tech tree in the next game.