I think it would be fun to do, but it is hard to determine the rules, as weapons, ammo and health is passed on from the previous levels. Maybe dividing it into the different chapters would be a solution, as you get new loadout at the start. It would be very easy to add to the leaderboards.

I think all should be on Hard. Easy is just the same thing, but just removes the need for planning and such. Sure it can be fun the enemies are easier to avoid, but the ammo(especially grenades) pickups are too good. Boss1 would be fun, but yea maybe only a race category.