Having recently completed Black Flag and AC3 and now making my way through Brotherhood I was looking forward to this one.
I've played it for around 90 mins and it's actually pretty good. With all the attention on the bugs, and there does seem to be plenty of odd things going on, the meat of the game seems good. I like the movement and the graphics and scale of Paris is impressive. Note, I've got a GTX 970 paired with an i5 4690 - I ran in offline mode as this seems to help the framerate according to reports. Only one small slowdown, the rest of the time it seemed nice and smooth. 1080p, Max'd everything apart from shadows and FXAA.
I'll probably go back to completing Brotherhood and hope this gets patched over the next few weeks, though in reality it will probably take months.
As an aside, I got my two boys Lego Batman 3 - that shipped with broken controls using Wireless Xbox controllers so I couldn't even it play it with them. Thankfully someone proposed a fix on the Steam forums - with TT Games releasing no patch to correct.