Well I think a lot can be learned from
www.splashdamage.com) and the work they did on RTCW ET.
Just simple things that make life easy for the average player is exactly what makes people happy.
Look at the demo recording system, total perfection.
You simply bind a key in your controls menu and not only does it do all the commands you normally would have to enter in the console or initiate via a script but it puts a "time stamp" on your demos so you can tell them apart easily and it also gives you a *very easy to use on-screen play back control system so you can actually skip/pause/rewind parts of a demo you are viewing.
Look at auto downloading.
In Q3/JK2 you generally had to limit it to 2/3 kbs or it lagged the hell out of a server.
In RTCW ET, same q3 engine but you can dl maps upon connect at 200+ kbs (not sure how they do this but it rules).
That would be a massive boon to the mapping community and get a lot more of these maps into rotation on servers if people could download them in a single minute as opposed to 30 minutes.
For those of you mod makers who are looking for some type of "project idea" for JA I strongly suggest you download RTCW ET (it's a free download and you do *not need RTCW to play it) and just look at all the things splash damage did right when they designed that game.
There a just so many “little annoying things” that I have hated about the quake 3 engine since it came out and SD really did a damn good job of simplifying and correcting a lot of those things.