Features I plan on the game having:
4 or 5 different weapons
Pickups
Different types of mobs
Multiple levels
Atleast 1 boss
Lighting
Doodads (with some of them being destructible)
Decent hud
Things already in the game:
Basic movement and strafing
Collision detection
Doors
A base enemy that makes it pretty trivial to add other types
Two different weapons and it will also be trivial to add more
Fog
Next things to add:
Decent hud
Ammo (and being able to run out of ammo and having to reload)
Better graphics!
Everything else.