1) Various types of alcohol, as inventory items, like 1?
2) Drinking contest minigame, like in 1?
3) Rubedo, nigredo, albedo, as in 1?
4) Places of power to draw power for amplifying signs, as in 1?
5) Fatalities (finishers) with other weapons besides witcher swords, much like the assassin's dagger in 1?
6) Ciri as an endgame marriage reward?
7) The vampire and dragon friends of Geralt?
8) Adda's royal ash for another striga and witcher style?
9) Another "relief stress" session with two women at the same time, like the nurses at final chapter, in 1?
10) Pissed off Shani to play doctor with her again???

Become a quest designer and add all the things:
http://en.cdprojektred.com/jobs/quest-designer/
:-)

But Ciri is almost like a daughter to Geralt, why would he marry her?

Because she loves him? And because in the official adventure module in 1, Eskel almost did that with his promised child, too?? (it got horribly wrong due to a curse, though)

If Lagardère can get away with it, why can't Geralt?