So, this one has been sitting in my library for quite awhile now.
The difference between factions is very pronounced making them all feel actually unique. Personal quests are somewhat uneven, some stages for certain factions are pure bullshit (have x unit of level x in your army and stuff like that). Minor factions are too inconsequential in general: they aren't very agressive at low levels and it's pretty much a no-brainer to just pacify them asap, most of their quests give too much for too little effort.
As far as basic gameplay goes: everything is tied too much to territory, you cannot realistically compete with few cities against other factions. There's also barely any reason not to expand as approval and dust penalties are pretty inconsequential 15-20 turns in.
The fact that even the most basic diplomacy is hidden behind research wall and taken into account how pointless the minor factions are, the game was designed to compete with other empires but the AI just isn't competetive from mid-game on.
The Ai just doesn't make use of all the different aspects of the game, they will barely upgrade their units, or pactify minor factions, they won't gather pearls, they won't expand cities when possible, some factions barely research past 2nd era.
Tactical battles are kinda shit. There are no usable abilities, it's all about positioning your units and using hard counters. Animations are slow and cannot be skipped, same goes for moving armies.
Overall, I can't help but draw similarities to Endless Space, in which the AI was complete shit as well but this one has a bit more going for it and should be fun in Multiplayer
P.S.: Shifters is a pretty good expansion, it adds a ton of new stuff, new districts, new mechanic, pearls to collect (auto-exploring units don't do that, btw
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