I cant play starcraft 1 in Gnome shell(to slow), in unity runs perfect .Why?
This could have to do with Compiz, it could also have to do with your graphics drivers, but I'm not sure which or if there's more that I'm missing.
Check compiz to make sure that the state is the same in both Unity and Gnome, and check to see which graphics drivers are in use.
I may be missing other variables at play here.
Edit: I just remembered that Starcraft doesn't run natively on *nix so you must be using wine -- check the wine settings for any differences when you run in Gnome compared to Unity.
mutter could grabbing 3d accelation from your card, and compiz doesn't , compiz has had lots of work over the years to help speed up full screen 3d applications