if you havent fired up duke3d lately, try this
this is just sooo superior to any of the fps games i tried over the last years
it's amazing
same with blood (edit: link) which is based on the build engine too, which might be even better (sadly there is no windows port however)

how come noone of the fps game developers came up with something equally entertaining since then?
the recipe is so simple
dont try making it realistic, start making it FUN again
technical revolutions may sell - but a real fun game that you dont only wanna play once to get kicks out of it, will sell even better, i guarantue you that