It’s good but not great. Better than launch Civ V for sure. My issues are that the end game is absolutely boring and the AI is hobbled by the ‘Civ Agenda’ system which the AI follows to a fault, meaning they weaken themselves (and the strength of the game) through self-sabotage rather than playing a basic game to improve their own position.
To compensate, Firaxis have added blanket bonuses and heightened aggression to the higher difficulty levels which only stifle play and narrow your own options.
The expansion from I have seen only seems to add additional systems that the AI will not be able to use effectively, much like the district system introduced in the base game.