I have not played Assassins Creed on the PC, but the controls are not bad. The aim key was in a awkward location, but I did not mess around with remapping, I already had a 360 controller connected and everything was right where I expected it to be, so I just started using that.
I have not done anything with multiplayer, but the singleplayer is done well. I am not really familiar with the Warhammer universe apart from some of the interesting looking miniatures I see at the local game store and Dawn Of War 2, so I have no idea if/how it fits into the lore. I can still follow what is happening and enjoy the story that is being presented regardless of that.