Pretty good, but
I bought this inspired bu the Brotherhood and I expected so much from it. Unfortunately, I was disappointed a little.
First of all, the game didn't work at OS X Yosemite before some update from Ubisoft. The resolution was out of screen before that update, so there was no way to get to options to change it. Finally update came and I could start playing it, after 4 weeks of purchase!
The game itself in okay, pretty good. But I didn't like the idea you have to use Ubisoft account to be able to play it. The game launcher is horrible, compared to Brotherhood. Enviroment is nice and places and citys/towns wonderfull. However, I didn't like idea that you have to ride with horse to another town. Distances can be quite long - takes too much game time!
The plot is a little different from the Brotherhood, but pretty interesting. Nice to see same loveable characters in AC2 and Brotherhood. Controls are worser in this than Brotherhood, guess only in Mac-versions. But still playable.
Basically, better than a average game with lacks in couple of things. If you like Assasin's Creed, I'm sure you find this enjoyable too.