In my opinion, you should focus on:
1. Gameplay/Level Design
2. Storyline
3. Graphics
my suggestions for Gameplay/Level Design:
1. Do not make large empty rooms.
2. If it can be set to static, do so.
3. If something would not realistically be somewhere, don't put it there. (ie. do not put a gun laying on the ground in some random location, put it in a weapon locker, or near a dead body.
4. use full lightmapping.
my suggestions for storyline:
1. Have the whole storyline thought out before you begin to work on a level.
2. If you must draw influences from other games, make it differ. no one wants to play too similar of games.
3. Express the storyline INGAME through videos or test pop-ups. (i recommend buying SignsIV to do text)
my suggestions for Graphics:
1. Make all textures seamless
2. USE FULL LIGHTMAPPING
3. if it is a small object, use a small texture size, no sense using a 1024x1024 texture for a book or other small item
4. make as much stuff custom as possible
"I admire its purity, a survivor, unclouded by conscience, remorse, or delusions of morality"
