hmmm where to start... the word detail is a good start... the rooms look like empty boxes? don't see much gameplay fun in walking in a box, so think of any stupid thing to brake up the box...
think architectural support, maintenance, pipes, venting,... give the space a destiny, a goal in life :wink:
also textures and lighting seem very dull. don't wanna spoil your moral but try maybe a smaller area to start putting al those hours in? like one building/house/street... something like that maybe.