I think what's more difficult to decide is how we'll manage the whole "gravity-changing" ability.
-The initial idea was that the player can switch gravity up and down, or even left or right.
-I think Georges idea was that the player can't do so by hitting a key, but only by hitting a switch in game.
-And if I understand txesmi (what does your name mean? I can never remember it :P) right then his idea was that gravity does not (only) switch by player action but by moving through special zones that have previously been defined.
Well I think it is not that difficult to combine those abilites.
Switches and special regions are more or less the same. One you have to use, the other one you activate by walking - this should be no problem at all to combine.
Later in the game, the player should obtain a gravity switching device, which allows to switch gravtiy at any time. This allows an increasing difficulty throughout the game (limited possibilites at beginning: easier)To limit this option, maybe argument that the batteries of the switcher cannot provide enough power for constant gravity switches and need to recover.
Of course this way a recharge feature could be added, but this might interfere with the time warp idea (power supply was not available ine arlier times). In short we should not focus on the recharge feature for now.
About monsters/enemies: for sure there need to be enemies immune ot the gravity switch, meaning they will not fall from the ceiling but just stay where they were.
To make the player aware of that, there should be some sort of automatic introductions - means as soon as a new enemy shows up the first time, the game halts and an info screen about the enemy shows up.
Same can be done for items and objects.
