Hi I love XCOM and as such I love this game too.
My intorduction to XCOM came through its demo, designed back when it was planned as just being a tactical game.
What got me into the full version of the game was how bloody hard that demo was and the days I would spend playing it to try to find an effective strategy. If my squad was spread out they would get picked off one at a time by an enemy with much better time units and vision. If I concentrated them into an inpenetrable group. I'd see an alien grenade tossed in wiping out half my squad. However, when playing the full version I was never really confronted with such a scenario, which was kinda sad.
ufoai has had some of that degree of difficulty: maps where you have to run across an area where there is no cover (alternating who's most visible and thus gets shot) 'cos you don't have the accuracy the aliens do at a distance to survive a sniping battle. XVI was a nice twist, but not something that nightmares were made of.
To that extent I'd like to make a proposal:
XVI outbreak mission:
This is the 28 days later (classic zombie movie made by the poms in 2002) theme – The spread of XVI will generally be an expanding area, hindered by government quarantines and topographical issues. The aliens can circumvent this by performing a UFO drop of XVI civilians in a populated area where XVI has had difficulty spreading to.
In the tactical mission 1-4 (depending on the speed of PHALANX response) unarmed civilians affected with XVI go around zombie-like biting other civilians and PHALANX members infecting them and turning them in, lets say, 2 turns. The goal is to kill all the zombies (thus preventing an outbreak and further spread of XVI) with minimal civilian casualties.
A twist on this is the question "How does one distinguish XVI and non-XVI infected civilians"? Only really by their behaviour (I'd assume the skin discoloration hasn't set in) and it is this factor that could set this mission up to rival the XCOM snakeman/cryssalid demo. Reaction fire will be useful as a PHALANX member will automatically shoot at an infected person who moves to attack someone. Strategy will be difficult. You need to get close to the civilians in order to protect them, but not so close that if they're infected they bite you and then it really becomes hard. Having to kill an ex- team mate before they are turned would really lower the morale of a PHALANX member, potentially making him start to shoot at any friendly he sees.
I don't see this as requiring too much extra work - a new enemy PHALANX unit, a zombie AI; however, the maps and artwork should be the same. I still haven't figured out a method to counter the simple strategy of just sending remote bots to wipe out the zombies. Maybe the need to keep the operation covert (thus requiring PHALANX to dress in civies and only carry pistols or knives). More thought required on that one.
If the player is not successful at this mission then XVI gains a foothold in a new area and the aliens then may even establish a base in the area. This may also be a good mission to introduce the player to XVI, as well as one to instil a few nightmares.
Greater blast radius for the alien grenades (this will make it tougher for bunched team tactics for PHALANX, but no real gain for PHALANX when they research it as they have to worry about collateral damage) is also something I'd like to see along with improved AI but is probably better discussed seperately.