Most annoying think in all shooting game is:
- Camera
- Keyboard interface
- Chatting
In my opinion, people would like to using mouse(for example to making keyboard hotkeys, managing GUIs, etc. ). Great example is changing current item by pressing item icon/use medikit by pressing icon. Another example in shooters would be giving orders(but not in all) or chatting(some special key to chat would be great).
Imagine this. I press t and write message. Some dragon is near. What can I do? Once I press esc, message would be lost in tremulous. It's some think, what I expect once esc is pressed on chatting.
When super key is pressed, tremulous should use keyboard as character input, mouse as mouse events input(click, button press, like in GUIs).
Another example is how to change camera behavior, but this would be another topic.