I really feel less inclined to complete games than I did in earlier Civs (except 5 which I felt less inclined to even load up).
I guess the issue with 5, and a lot of Civ games, is once you know how to beat it, it becomes hard for the game to actually challenge you.
Then once you choose a harder difficulty, the game becomes unfair instead of just harder.
For Civ5 this is my genuine opinion of its biggest flaw - so for example Happiness.
On easier difficulties, the higher default Happiness actually opens up the strategies and makes the game more fluid and fun, letting you experiment more with wider and riskier builds than usual.
But of course, the AI is easier, so the game becomes a bit more boring.
On higher difficulties it was the opposite.
I think Civ games in general suffer from this problem where they only know how to make the game more unfair instead of strictly more difficult - and on difficulties like Deity, even for Civ6, the game just becomes playing the 'meta' strategy so that you can beat the bonuses of the Deity AI.
This hurts their replayability, because it's all well and fun to play every single Civ and Leader until you master their playstyles and have a lot of fun with the maps -- but if the AI cannot ever challenge you fairly, then the design will railroad you into one particular playstyle until you get bored of the game.