As far as I understood it it still works with the classic Xcom mechanics of you shooting down enemies-playing tactical battle-repeat with you getting penalized for every missed enemy craft, right? Or you choose your own tactical battles?
That's basically it. It's clearly jury rigged over Xcom. Not every mission you miss is a penalty, but you quickly fall behind if you skip missions. As you move up the tech tree, harder missions become available and easier missions stop appearing. This makes recovery a bitch. Keeping ahead of your finances is also a problem.
I don't know if it's been fixed, but it used to be playing on lower difficulties penalised you in the long run, because less loot = less money and science progress. The real problem is OG Xcom's healing and shooting mechanics making recovery take months for a single gunshot, and unlike OG Xcom where men are dispossable, you need to keep sending guys out to keep pace with the threats. At some point, the game snowballs and there's no real recovery. Again, at least for me. Even with the fan made easy mods, I still suck.
Edit: I forgot to mention. The tech tree is huge, but it's easy to miss something vital. I've lost campaigns because I didn't unlock craft weapons or a hull that could mouth them. Even then, craft like the Little Bird, while cool in concept, are utterly useless in practice. So you can softlock the game by not choosing the correct 7 tech from a list of 300.
I loved XCOM and liked XCOM 2, but hated War of the Chosen
War of the Chosen has issues. Not least of which is I've yet to do a run that didn't screw up the story. The zombies can be fun to fight, but sometimes it's a slog. And yeah, some bosses can be bullshit. I really like Templars though. There's also some really good mods for it too.
Xcom 2 vanilla has issue too. Those walkers are always glitching out. And those stun guys running out of the fog of war, 1 hit koing a guy, and causing the whole team to panic so you can only watch as your squad gets wiped is no fun at all.
Oddly enough, Pheonix Point does faction play better than War of the Chosen did, since pleasing one means pissing off the other two. In WOTC, there's no downside to getting all of them to like you.
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While I'm replying, might as well expand on Pop Up Dungeon a bit.
The gist of the game is a tactical game where you start as a DnD party, and have to go up a wizards tower. Each floor is a string of combat encounters. You level up your guys each run/floor, but they reset after a run/floor. However, you get pins for your necklace that grant up to 5 buffs. These vary in power and rarity. It might be more health, health regen, more cards on level up, etc. There are side stories that vary from a few dungeon encounters to full 6 hour RPG story with space battles.
The characters also vary. You have typical DnD stuff, dwarf, paladin, wizard, samurai etc. But you also have Apone from Aliens, a red shirt from Star Trek, Doge, and more. Some characters are clearly stronger than others. The game relies heavily on user made content, but lacks the player base to properly support that. I remember the stock space campaign being really fun. Though I never finished the wizards tower.