first of all, you use ww2 stuff, and the enemies are robots ?
bit strange, and it not looks like a city, you want tips? hmm okay
first i saw fire, but you cant walk in it, why dont you make a hurt ozne in fire, so the player can walk in it
use ww2 enemies that will look better, play with ambience, if the player walk in a cave, use a trigger zone to chanche the ambience to dark, if he walks out the cave the light will turn on.
use some more entities and explosions, like this : if the player wants to go to left he first needs to shoots some barrels to clear the way.
use cool sounds, like an enemie who is hurt or a cool ingame music. use cutscenes to tell where you need to go.
and i can jump out of your level -.- search on the forum for a invisible wall.
you use the lightmapping good!
place some allies and more enemies, it was easy to reach the end of the game
try to make a story line, and make objectives like find the enemie leader and kill him, also you can use scripts to make your game more fun
i hope i helped you a bit.
cheers mgarand