Your map doesn't need every single powerup. Sometimes just having one or two is plenty. Impact Hammer jumping for an armor vest isn't worth the effort. No one will go for that. There is a direct correlation between the size of an area and what weapons are effective in this area.
Tighter areas make the flak more valuable, more open areas make the sniper rifle and minigun better.
The homing mechanism of the RL is very useful in large areas as well. Let decorative actors do the work for you- use light fixtures, sconces, and pipes instead of building them into your world. The location of playerstart, or spawn points, should not be an obvious thing to players. You should do this with weapons, but if you do it with playerstarts then you're only encouraging spawn killers. I really loathe walls that slope up and away from the player.