Imporant first:
-Improved HUD (seperate chat and other stuff so chat stays longer)
-Better sound, foot steps, the grunting jump noise, as mentioned, the pbcup bug
-New level system++ this will make the game look new and attract many new players.
-Improved player models
-view wep on player models...
-Dont know if this is possible, but when someone drops a gun or anything else, make it more instant. ditch the tossing the gun in the air effect, which appears 2 seconds late anyways.
less important:
-visable paintballs
-easier to ID teammates. even, No ID on enemies, and make teammate ID pop up quick.
-If you EVER improve the GUI, look at TRIBES2. It has one of the most impressive interfaces and is simple to use. Chat, email, Ignore, bio, rankings, etc...
-which also means user logins to play. I'm for this, but I suggest each login has 3 or 4 names they can play under, and searching in the super new GUI for that name will show all that players names.
-locked FOV (I know people would hate this.. but I find FOV changes sorta cheaty)
-make the guns stop shooting above the x-hair. it should never go above the x-hair...