I run the client in linux mint 17 which is 14.04 based. At first I had terrible performance, then I found that the standard mesa driver for the intel GPU was not hardware accelerated. When I installed the intel graphics driver all magically fixed itself.
Do you have the correct driver for your graphics?
im using the fglrx-update ones, the non propietary ones dont work (actually they can render most of the game except water, OP items and yelk backs)... guess i could try with the fresh version from the amd website,