Ok so I played for a couple of hours last night and..... I'm really enjoying it!!
Ok so it has some tech issues - you can hardly miss them - floated on a roof for a while - and yes there's frame rate issues but, fundamentally, the environment is staggering and unbelievable interactive, it's visually superior to any previous AC game and the movement is vastly improved - wait til you try descending without having to hit circle every item you want to drop down....
And, personally, I love that it is less prescriptive - I don't want to be told exactly where to go next or have to do everything in an entirely linear fashion - I like wandering a little to see how it all unfolds. The level of interaction with people and surroundings is vastly better - you don't just climb facades any more you can enter and explore a lot of them. Some of the new gameplay techniques are better too as is combat
I could go on but what I'm trying to say is that I am not a tech geek who is completely hung up on the graphics etc (and I get why it would do the heads in of people like that) but what kills a game for me is if it continually freezes and falls over or is impossible to control the way you should be able to and Unity so far hasn't done any of this for me.
One thing that bugs me is the pressure developers put on themselves, having announced a launch date, to develop to that release date to the point where, in the end they compromise on their initial intentions. I would love to see games fully developed then release programmes planned when it's almost complete to cut out this initial launch problem crap.
Then maybe we'd all be raving about the visual quality, improved gameplay and the hugely ambitious level of environment interaction rather than bemoaning the crass technical failings.....