I had some minor issues running the game as a normal user on my Gentoo desktop with nvidia-glx drivers.
./paintball2 was failing while trying to load libGL.so
I created a link to the libGL.so in my /usr/lib/opengl/nvidia/ directory and it worked fine.
On another note, I encountered two bugs and one inconvenience dating back from my days of an admin on linux servers.
-The binds associated to kp_* only work on my configuration(MS Internet Keyboard, default keyboard driver, XOrg) when numlocks is off.
-Backspace/Delete only work one character per press(cannot hold it to delete multiple characters.
-Filenames are case sensitive - a real pain for multi-cased map names
Other than that I can say that the client runs great on my system just like it did on my previous XP system.