You all have some very cool ideas there. I think we should not use them in the first levels though, as they're quite complicated to solve. I think in the first 10 levels you should only be able to play the sister, and the first 3 should be very simple to intruduce the player to the whole concept of switching gravity.

Edit:
BTW, I know this is not the step we're at right now, but I'm interested in it: Will we use shaders? I believe we should, even if it's just simple wiki-shaders. Normalmaps and Spec maps would make the game look much more detailed... It would mean we couldn't use simple block geometry though (which I wouldn't want anyways).

In fact, I'm just noticing I don't think we've talked about that at all so far: Blocks or Models? I vote for models. They simply tend to look better. And with polygon collision only active on the needed parts, it shouldn't be hard to do. Also, we can then start making lots of models and people can place them in the level and re-use them (like a set of staircase, or a window or wall). Also, we can make them in any program of our choice, and don't have to use WED-only.

Edit 2: I'm working on a sketch also, just to let you know I'm not slacking off entirely