Tremulous as many people know has great game-play, it is free, and all of the other features.
However, as most of us know -- the IOQ3 engine is old, and it pales to comparison to any (somewhat) modern engine.
There are three ways of fixing this issue: Pretending it does not exist, modifying the existing engine or porting it over to a newer engine. As before there has been discussions regarding this issue, however, perhaps someone has an idea that will not include porting the game to a closed source engine or some other ridiculous concept
Single features being added to the current engine may be a plausible and worthwhile action.
Examples include (everything should be skillfully used in moderation) bump mapping, parallax mapping, bloom, better map lighting/color bleeding, smooth shading, and such.
Perhaps we can slowly add various upgrades that will improve the visual appeal of the game?
Yes it is a bandage, however, anything is better then nothing.