This game is FULL of bugs. For example, if a world war starts, or a big country like the US surrenders to you, a incredible lag happens. I have a good gaming rig (BC2 runs on max without lag), so its not that.
Its really annoying being handicapped, worrying "Should I attack? will it lag for no apparent reason?"
And another one I found out, if you zoom near a city to hear the city sounds, sometimes it gets bugged and the sound loops and repeats again and again and you can only fix it by either zooming to another city to hear its sound or completeley exiting the game (it will continue to loop even on the main menu)
On top of that we have ships that seem to somehow go bellow the land and airplanes that just float in thin air.
I haven't really tried multiplayer much, but its probably buggy too.
This game to me looks like a beta version. If the bugs are removed, it will score within my "best strategy game of the year" place.
I havent had any lag since few patches ago, try to defrag the game\drive, or just a clean install, remove old saves.