When I install gnome 3 from ubuntu software centre, I feel it is too slow and the windows decorations are not clear. Can someone help me?
Can you check which version of GNOME3 you have installed? The version you get from the Software Center is probably more than a year old.
If you cannot find the version in the Software Centre, run instead
which will indicate which version was installed.
I think a good option is to compile GNOME Shell. May sound daunting, but it's quite easy (no skills required) if you follow the instructions at:
The most probably cause is that you're using proprietary drivers. Both nvidia and AMD users have problem(e. g. me :] ). If you want to try GNOME Shell, try to run it using opensource drivers - nouveau(for Nvidia) or radeon(for AMD). Intel should work flawlessly out of the box :)