FPS game mode for this. Only time will tell if it will be fun or not.
But here is how it is done. Options -- keyboard/mouse scroll all the way down and enable dev mode. (the check box) hit the ` (by #1 and tab) type: map lobby Type in each of the follow words without quotes, in ( ) i will say what it does "firstperson" (first person mode)
"asw_hide_marine 1" (you really play over the should view, this removes the marine from view)
"asw_controls 0" (this removes the "dumb movment", normally w is "north" cause you are stuck in "north = up" mode, but in first person you can turn and look different ways, so w is no longer north. This makes wsad movement like normal FPS.)
you cant use fps in servers (Bcuz sv_cheats must be enable).