CK2 is finished, done, dusted. The game was effectively finished at release
Was it now? Without retinues - it was quite incomplete (TBH I would say that retinues should actually cost maintenance money, but be 10x cheaper then mercs.), without ortodox religion features - it was quite incomplete. Not having playable Muslims could be ok, but adding them as a playable side makes the game much more interesting.
Now, the game does not have long-term relationships between the dynasties, thus I can press Hwice badly, and a new-born Hwice will not care about his father, grandfather and 3 patriarchs before them, who died in my dungeon. If my ruler dies - all those hard-pressed Hwice will say: "OK, your father was a bastard, his father was a bastard... but we belive you will be kind to us, we will help you to rule...."
I would say it is incomplete.
Pope is a randomly generated character. He is sometimes a cynical sinner, who cannot care less about christ. Well. that would be possible within a timeframe if he had a powerful allies (think Alexander VI), but not having a proper curia mechanics makes it seem incomlete.
How about the rise of the trade republics? Venice, Hansa, Genoa... all rised during this period.
And the cadet branches?
My grudge is not for releasing a fantazy DLC, but with the priorities. It would be cool to have such DLC, along with a Knights vs. Zombies DLC, in the end of CK2 lifecycle, after all the mechanics is updated and all the controversies are fixed, at least at 1066 start date.