I would like to point at a certain problem with sins that prevents me from enjoying this game fully in beyond-early-game scenarios. The problem is not the graphical/FPS lag that comes with all the visual goodies or the amount of stuff that needs to be processed. That's well understandable.
The problem is the input lag, the asynchronic processing of clicks and mouse movements.
As an example, let's say you have three buttons on your screen:
[A] [B] [C]
If you quickly click your mouse on each of those buttons (move pointer over A, click, move to B, click...), the output should be: ABC.
That's how it normally works, until battles get big and the game starts to lag. When this happens, the mouse and the clicks start to be processed at what seems to be different priorities.
So if I try to quickly click ABC during a heavy game lag, my first click (on A) would actually get processed AFTER my mouse pointer is already over B or even C!
For some reason, there's an increasing lag on mouse clicks (and keyboard input) that comes with the general lag, but it seems there is NO LAG on mouse movements!
(or, at least, it's significantly smaller)
End result : I have to hover my mouse over the target for a second every time I click in order to have the click processed properly.
Now, it wouldn't bother me as much and I could just get along with this as a natural result of the general graphics lag, if not for one thing....
.... Blizzard somehow prevented this in Starcraft 2
Yep, SC2 does not have this issue. Even if the game lags like fuckityfuck (for example, the first 3 seconds of a game are just pure lag and most big fights, at least on my PC, are lagfests as well), even if the screen is COMPLETELY FROZEN for a second or two, all of my mouse commands are processed EXACTLY how I clicked them.
I believe that if this one little thing could be fixed in Sins or at least prevented from returning in the sequel, it would make the game a LOT more enjoyable.