While I think the quality of single player Assassin's Creed games have gone down with Revelations (which was just decent) and III (which I think is bad), I still really enjoyed the multiplayer in both, and think III made some good alterations to the elements Revelations introduced that I thought were a little half-baked. (The added priority of stuns really changed the dynamic of playing defense, and changing kill and stun to be the same button in III so you don't immediately know when someone is your pursuer fixes that. I also think the changes to abilities and their cool-down periods helps balance the game.)
I'm not usually huge on multiplayer stuff, but I absolutely love Assassin's Creed's multiplayer, and if Ubisoft released a multiplayer focused Assassin's Creed game that included enough content to justify the price I would absolutely buy it. What about you?