Several things relating to making the upper dungeon feel more “eroded” or exposed to the elements/other adventurers, in keeping with NetHack flavor that other people have been seeking the Amulet:

• Falling rock traps on shallow levels come “pre-disarmed”, which is to say that they have already been used up and so should consist of a pile of rocks on the ground underneath a falling rock trap with no rocks left in it.
• Rolling boulder traps on shallow levels generate without boulders or with out-of-line boulders.
• Traps with ammunition can have a few pieces of that ammunition lying on the appropriate space.
• Dilapidated armories.
• Monsters on these levels are likely to generate with zero-charge or low-charge wands or other items.
• Fewer items lying around.
• Randomly destroyed walls.
• Fake bones piles (see below).

Note that this has been partially implemented in 3.6.1 with the addition of fake bones piles that come with a pre-disarmed trap if applicable, although that was aimed less at adding ambiance and more at helping players avoid early traps.