X Com: Enemy Within, all the way. Basically you manage the world's resources to resist an alien invasion...
THIS CONTAINS SPOILERS
So there comes a point where you have to make judgement calls like: "Do I let Australia go in order to save America" etc. So there's some great moral dilemmas as well as general strategy of research, whether it's ethical to use bionic soldiers who can't be changed back etc.
The battle scenes are turn based and done using the Unreal Engine so look very cinematic. And the difficulty curve is insane: one minute your soldiers are gleefully blasting Greys to smithereens as you laugh at how easy it all is then the next minute the squad is running for its life after half of them have been eviscetated by gigantic insect creatures and the others have been turned into almost unstoppable zombies!
There's some great world building. For example, if you don't protect a country very well then criminal factions cut a deal with the aliens and start to undermine you and even fight you... and if it gets REALLY bad the population actually start to worship the aliens!! (Although in all my games Canada seems way too keen to do this)
Thoroughly recommend it, if you love Aliens or Sci Fi in general you'll love it. Favourite moments so far:
Mexican stand off where the fate of the world relied on my squad surviving and I only had one soldier left. I had to decide whether to take cover or fire (she had hardly any health left), she shot at the same time as the enemy and... hit them and they narrowly missed!
A huge mothership arriving dwarfing everything and in a Day the Earth Stood Still / Harryhausen type moment a terrifyingly gigantic enemy ambles forward to the dismay of the ground team.
It's expensive at £10 on the App Store but I'm still playing it a year later!