1.reflection and refraction. for a game so technically advanced, it's a little sad to see such disappointing water effects. and i'm sure many of the weapons would look much better if they had some ability to reflect their surroundings.
2. animated textures. not just for the water effects, they'd make for some great explosion and smoke trail effects as well. because you would no longer have to rotate particles to make the smoke seem dynamic, you can make the bottom of particle texture darker than the top, to give a a great illusion of thickness. as shown below in an image i created using anim8or (free 3d animation program).

3. radiosity. this is something extremely expensive to compute. however, i thought of a great method to fake it quickly and inexpensively. i'm surprised it's never been used before.. if you can incorporate reflections, you can blur the reflection a huge amount, and get a radiosity effect. for those who don't know, radiosity simulates light bouncing off of surfaces and onto other surfaces, thus if you put a whit ball ear a green wall, the white part facing the wall takes on a greenish color.

obviously this isn't top priority, but it would look pretty freakingsweet, you'll be hearing alot about it in other games soon enough.
4. Relative physics (inertia). this shouldn't be too hard to incorporate at all. i can see how the development team might be iffy about this one, so many people are used to playing nexuiz without it, you cant just change the behavior of the game. well, i think it would be fair to allow the user to choose if they prefer to play with or without inertia, it's not like one player will have the edge over another for having inertia, it just lets people be more comfortable with the game environment.
5. dynamic bloom (aka fake hdrl). this shouldn't be too difficult, have the bloom intensity adjust according to how bright the overall environment is, cheap inexpensive way to simulate hdrl.
6. more widely used model format. i'd love to help devlop for this game (i'm an artist as well as a 3D animator), but i the very thought of having to install and learn 9 different programs to create and animate a character model terrifies me, and god knows this game needs new character models. maybe make it more compatible with blender. my dream would be to make it more compatible with anim8or, but you dont have too large a userbase there. haha.
7. motion blur. alright not at all important, but still cool

8. fullbright off! for gods sake, let it be up to the player if they want to turn full bright off on a server that has fullbright on by default. fullbright looks unbelievably ugly, especially with bloom enabled, it's really inconsiderate to mandate fullbright to those of us who are graphics junkies.
9. support for voice chat?
10. a better way to zoom, the current way seems to keep the mouse at the same sensitivity as if it weren't zoomed. this turns a mouse acceleration of 2 pixels into a mouse accelertion of 10 pixels when zoomed, absolutely terrible for using the nex unless you have an uber dpi mouse (i do, but not everyone else does).