Spike traps: We already have floor crates in LOG1. It would be cool if there were spikes suddenly extending from some of them. There could be a new rogue skill - trap detection or disarming. Besides the obvious disadvantage of losing some health, it could also have other mechanics, like keeping the player in place until the spikes retract. For extra challenge, the trap could keep the player in place and not let him even rotate. Not a good thing if you're trying to run away and have an ogre behind your back.
Pillars that rotate: A long time ago, when LOG1 expansion was planned, AH posted this wonderful screenshot. Look at the pillars to the left and right. I immediately thought that it would cool if each segment of that pillar could rotate. There could be secret compartments there or there could by some runes on it and setting up the right combination would open some secret passage.
Guilotine trap: We could have a guilotine trap, similar to what was in Prince of Persia. It would enhance the gameplay a lot, because it could be deadly to the player, but also to the monster as well. This could be a feasible strategy to lure powerful monster into this trap.
Movable objects: Some of the objects in the dungeon should be movable. Phit's mine wallset featured coal cart. It would be great if it could be moved. AH teased us with an egyptian style level with sarcophagus. That sarcophagus should be movable to reveal something behind it. (Speaking of which, I really hope it will be possible to open it up and see what's inside - treasures, stale air, or a mummy).
Chests: Several mods for LOG1 implemented chests. If they are locked, player immediately imagines riches inside. Chest is also a capable concept. You can make them pickup-able. Player can carry them on if he doesn't found a key yet. They are heavy, so there's penalty for carrying them around. Chests could be movable, so they can be pushed sideways to reveal something behind/under. Imagine a story where player finds notes about a treasure hidden in a chest. After a long search he finds a key and there's only a note inside "you used your mind, now it's time to use your muscles". The chest can be pushed sideways to reveal the real treasure underneath it.
Breakable doors: Some door should be breakable, e.g. rotten wooden door or even glass doors. Because it's fun to smash things. See Germanny's DM wallset for example.
Rolling huge ball: If you are not a dedicated Indiana Jones fan, you should leave this forum immediately
There's a mod for LOG1 that has such a ball. It's awesome, because besides being cool, it also forces the player to move quickly. The ball could either squish/kill or push the player. Or push and hurt a bit if it's a spiked ball. There could be a long corridor with many alcoves (most of them empty, but some with loot) and a rolling ball behind your back. Similar effect could be achieved with a wind simulation. There could be a narrow corridor and a wind blowing that pushes the party towards some danger (cliff or a pit with fire).
, you can use clothes to cover them or use spells to take off light source nearby 
