Well, got the opportunity to play AC:S for couple of hours:
Sigh...honestly, I feel that AC:U (patched) is the better game here. This just feels so...old. Like almost nothing has changed for the better. Lighting is so much worse now than in Unity, and it can really be felt especially atmosphere wise. Character models...same thing. Jank...as bad as ever. Missions...same boring shit with the same shit AI. UI...you guessed it - NO, actually it is somehow WORSE...luckily you can adjust the HUD though. Unity at least had some "next-gen" things going on...actually the closest I would compare this game in many ways is Revelations.
Sure, there are some (not many) new ideas but they lack any impact because the general feeling is so "last year". Anyway, can't say that I'm disappointed as I had no expectations whatsoever. 6-7/10 game...at best
EDIT: Also, one thing that really gets super annoying is the repeating enemies. Sure, it's been the same in every AC but here it is somehow worse than before. You're fighting that big bald dude, the female one, the cane ones etc...all in the stupid same red outfits over and over again. Especially because those red dudes are everywhere in the streets and attack you on sight...seriously this is not cutting it anymore in 2015 - not when many other games do it so much better. I mean come on even in Batman: AK there is more enemy variety and that itself could get quite repeating/annoying.