Due to the thread necro warning I got when I went to post in the other thread about this (from '07) I'm starting a new thread.
An improvement to the mapping system would be nice. What you saw is what the map displays after you leave LoS until you come back. So even if barrels explode and destroy items/walls/etc the map still displays the barrel/walls/items. Doors stay closed unless you saw them as open and didn't close them. Items stay on the map, whether or not an enemy has decided to grab them/stand on them, or something has destroyed them. Makes more sense to me anyways, and it might up the challenge a bit with the doors and walls, but I still think it'd be better. Plus trying to remember what room I saw (insert power up name here) in gets to be difficult in some stages. Also remembering the last location you saw an enemy could be plausible. Example: "I remember seeing a Hell Knight beyond this door", so until you go back and verify whether he's still there or not, it remains on the map. You could even get evil with this, say the Hell Knight moves, and you see him somewhere else, you run, your map now displays the location of two Hell Knights, though it's just one moving around. Panicking, you head down the stairs and all the items you could've grabbed and the exp you could've gained have just gone right out the window.
Of course, items and barrels could be something you only remember after a couple levels of Cat's Eye or Intuition. For example, a new advanced trait called Eidetic Memory (or even a new base trait to replace something else or added to the game).
Either way, level 1 could be something like remembering barrel locations and ammo. Level 2 would be remembering non unique weapons/items/armor/powerups. Level 3 would be remembering the locations of uniques.