I too have been experiencing unstable gameplay since the last patch, but nothing to the point where it's unplayable.
First make sure you meet the requirements to run this game, that can be found here
Second, Make sure that most background processes are closed, and definitely make sure they aren't using an unnecessary amount of PC resources (for example, sometimes my Xfire, Yim, or Skype use a whole cores worth of processing power, which is not normal). Those can cause the biggest slowdown.
If after closing most of your background processes you are still experiencing lag issues ingame, don't hesitate to send me a PM and I'll look into this matter further.
thanks for your patience and understanding
Edit, also I know this is a Ping related issue, closing background processes somehow effects ping (don't ask me how) but most importantly make sure that all instances of akamai netsession are closed, as well as awesomium after running AVA.
I would also look into seeing if there's any connection problems going on at your end, check Router and modem connections, and restart them if you have to. Possibly even give your ISP a call. It's probably not the case here, but it's always worth a shot