How is this going to work? Will the second playable character only be used at certain plot points in the game? If so will this second playable character be able to roam the open world freely?
This is a really big issue regarding story. I bet that the second playable character will be very restrictive and more of a nuisance to play than just playing as Geralt through the whole game , if that second playable character doesn't have his/her own campaign.
I imagine this is exactly how it is going to work. Pretty much used in exactly the same way as it was in TW2.
The assumption, and hope, is that they will have learned from TW2 and make it so that when you take control of another character, it feels good and if the character has new skills/abilities, or more importantly can't do certain skills Geralt can, then you will be notified as to not make controlling that character a pain in the ass.
Honestly I loved the sequences in TW2 where you got to control another character in regards to the storytelling and character building, the only issue was the aforementioned control problems. The characters had an extremely basic "soldier" move-set, which made them feel very clunky, and not being able to evade made the scenarios problematic in that sense.
So whether or not the playable character in TW3 will be a "nuisance to play" will entirely depend on how it's implemented, and hopefully they'll have learnt from TW2 and improve it. As for the Story, I don't see it being a big issue at all, as I said I felt moments were enhanced in TW2 by being able to play as those other characters, and presumably it'll be used to even greater effect in TW3.
They've said that Geralt is still the main character but there will be a "substantial" part of the game where you don't play as him (I'll see if I can find the source for that, it might have been on IGN or something; I hope I'm not just mixing information).
I'm guessing it's going to be Ciri, but it could be Yennefer. Still, deep down I hope it's Dandelion again.
I'd so would want to play one of sorceresses, I hope they can make this work... I recon it will be one of the other Witchers and/or Ciri, though, since they all use pretty much the same weapons/animations, I guess.
I really think it's gonna be Yennefer . I feel it'll be like in the books where she and Geralt do what they can from both ends to find/protect Ciri. Also when she says "only you(presumably Geralt) and I truly know what all of us will soon face" I feel it really puts her right in front of things. Besides, she got her own trailer/intro sequence and why would CDPR give an alternate look as DLC to a non-playable character?