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-Needing to install 10 mods, bare minimum, for it to approach something functional and playable? And this is coming from someone who got through Enemy Unknown with no mods!
-Trying to be a stealth game even though the sight and patrol mechanics are atrocious.
-Psi powers sucking
-Falling into the same difficulty hump as Enemy Unknown. The very beginning of the game to the 30% mark is the hardest part. It's downhill from there. From the very first mission: every enemy has enough health to survive a grenade, you're limited to 4 soldiers, and sectoids can mind control you in addition to being damage sponges AND raising zombies from the dead.
-Money being ridiculously tight. They also overcomplicated the economy; you have to have uplink capacity AND supplies AND intel to expand regions. Money is so tight that research speed and scientists are totally pointless because the bottleneck to getting new stuff is always money, not research. You will research things long before you can afford to build them. You will also never be able to get half the stuff available before the campaign is effectively over.
-They flub the theme so frigging hard that it ends up feeling like the exact opposite of what they were going for. The Earth is supposed to be occupied and fully controlled by the aliens while your group is a guerilla band. The intro movie gets it right: blending in with the civilians until you can blow up security points. Yet in the actual game your guerilla group flies around in a quarter mile long heli-carrier, tries to sneak through cities via a giant noisy drop ship, and are completely unable to blend in with the civilian population which rats you out to the aliens the instant they spot you. It feels way more like humans won the first game, captured an enemy battleship, and used it to invade the alien home planet as they fly around unopposed blowing up their cities.
-Dear god the performance. How is it my computer runs The Witcher 3 on medium settings over twice as fast as this grid turn based game on low settings?
-They tried to make the strategic campaign seem more like the original X-Com where the aliens build bases and you try to to keep pace with their incursions. But it really is just the same "arbitrary 3 hot spots and you can only respond to 1 until a meter says you lose the game" as Enemy Unknown. They do a decent job at trying to hide that fact, but it's still there.
-Out of all the things XCOM fans wanted to see in an expansion, who the fuck even began to imagine that "bickering sibling bounty hunters" and "rival infighting human faction" should make the list?
Just...bleh. I played through Enemy Unknown twice before uninstalling it. I petered out two-thirds of the way through XCOM2.
Firaxis has been shitting the bed ever since Civ 4 Beyond the Sword. Civ 5 was a disaster and Civ 6 went the same way as XCOM 2: doing a decent job making you believe they fixed the main issues with its predecessor but it's still the same mess.