Personally I miss Ezio. He's one of my favorite video game characters of all time and he was a ton of fun in V. I'm glad Geralt is the guest for 6 but I do like Ezio more. I was cool with most of the cast for V except Patroklos.
At first I hated them all since they replaced the originals but the newcomers were not bad when given the chance. If they were more fleshed out it might have been better. I just can't like Xiba's food schtick. Going from Kilik to him was impossible.
Mechanically they're great especially with Ezio and his multiple weapons but I'm neutral about the guest characters in general. Never really cared for them since I have always bought SC for the SC characters.