zero 43 sure you can
you can make a level however you want you to have the folowing on the game to the folowing:
have the main emenies be zombie and robobots
dont make the zombies have too much life but make them fast and hurt hard and have some that can re spawn
have at least one puzzle or challage
have one really strong boss
example:conker,aiko,armyman etc. etc.
with alot more life
keep in mind this is a horror/scfi
but keep it that a parent can watch it without geting x rated\
have a suprise
these r the reqiments for level devlopment or level designers
Fps Creator Forever!!!and ever and ever and ever and ever...