floors and ceilings are a bit to one dimensional. Some contrasting in elevations and depressions would go a long way.
good point, break up the floor and ceiling with some steps and some grates that look down onto some pipes.
as for your lighting, it needs more contrast. Take out ever other
ligth in the hall way so the pattern of the wall and floor break up a
little and the player gets a better sensation of moving with the light
and dark falling onto his gun.
You could also use more lighting colors, and types of light.
i've been told that the best way to do this is with a 3 point lighting
system. one strong light (like the combine light or a spot light)
one set of soft lights (florcent [sp?] or wall lights) and one bright
point light (like a fire that cast orange light all over the
room). This will leave good shadows withouth alot of pure black
and it will also add quite a bit to your rooms.