I'm really looking forward to AC Unity. I already preordered the Bastille edition. I mean, I was very disappointed with AC IV Black Flag but I have hope for AC Unity. First reason is that they returned to cities and vertical gameplay (now even with indoor areas), second reason is that they set the game in one of my favorite historical periods and third reason is that they hired the game director of AC Revelations for Unity again (and Revelations is my favorite AC game because of many reasons)...
I don't have much problems with the co-op. I probably won't use it much (I just lack the friends who play AC as well, sadly) but I also don't think it will drastically diminish the SP experience. This time they seem to to focus on SP and co-op and cut the MP so they don't spread too thin. If I understood the co-op mode correctly every player plays Arno in his game and your co-op buddies will just act as support without any interference with the story. So you can just hunt down the bad guys alone or in the group, it doesn't matter to the story because in your own game you're the only important person who does all the talking and if you join the game of a friend you act just as a supporting character during a mission. I think MP will be quite similar to the MP in Watch_Dogs where also everyone plays Aiden in their own game and they appear as different persons in the games of the other players. That's also the reason why there are no females in co-op because everyone just controls his own main character and because it's not a seperated mode but just ingame hop-on, hop-off MP/co-op.
I just hope that Unity will be less driven by numbers. In their latest games Ubisoft pressed their open world in numbers, labeling everything even the secrets. I would appreciate a less formulaic and static game world in which most of the game is centered around the next achievement or the next set of stuff found. AC Unity should be centered around the main character and his story again and the open world should be his authentic playground to fulfil his destiny and not a place in which 50% of the game is centered around finding labeled and numbered collectives. You've rescued a citizen? Nice, 9 to go. You killed a carrier? Nice, still 7 on the list. You've found a flag? Ok, still 45 to go. Watch_Dogs and AC IV were horrible examples of that formulaic approach in which the open world were not used as a natural and dynamic world but as world in which every dynamic or exciting moment is ripped off and you could always have a look in the menu how much there is left for you in the game....
Well, we'll see how they'll do it for Unity. I don't expect too much or I guess I will be disappointed again. But as an AC fan I will play it anyway, if only for the missions and for "visiting the revolutionary Paris"...