one thing that comes to mind is that 90's dos platformer shooters have resources that are mostly used in the short term. like, the main gun doesn't upgrade much, and superweapons have small ammo capacity.
if i want players to seek out loot, it needs to have long-term significance. otherwise it isn't worth the risk of trying to get anything.

... i'm not sure how powerful a player character should generally be compared to most enemies. or what the enemy density should be.
having a harsh timer ALONG WITH enemies taking time to deal with would just be unpleasant.
i guess that's something to experiment with.