I was going to post this as a response to Squish, but I figure I might as well just toss it here and see if anybody else feels like nattering on about it.
One of my main reactions to Terry when he told me about his idea for squish was a real excitement that, by going to a 2D perspective, he had manage to reproduce this mechanic of dimensional reduction without requiring, anywhere in the game play the player to change views to look at the various squishing possibilities* (this was the ideal of the game where there were vertical and horizontal squishing possibilities allowed). This was significant to me: I wouldn't have idly thought it possible to separate out the two mechanics of projection on one hand, and of frequent view-changing on the other.
I haven't played crush too much, and I don't know how Fez is going to handle this, but at the back of my mind I always have sort of reservations about this mechanic of projection as being potentially very unintuitive (in practice, I find that the levels of squish can also behave in rather hard to grasp ways, but at least one can see everything at once in principle).
There's also another game I'd like to bring into this, as a sort of natural complement to these sorts of games,
PoV, a puzzle game where one is given the profiles of the various projections of a 3D object, and has to reconstruct it with a limited number of blocks.
In my head, I tend to classify the geometry universes of modern games into 2 categories: observer dependent (Echochrome), and observer independent (Portal)**. Games like Crush/Fez seem to rather undercut such a classification.
*actually, I did provide a tiny amount of code to Squish that rather undercuts my own point of view of this game, which represents the squishing mechanism for some blocks as a rotation through 90 degrees about the horizontal line the player is on.
**I can't think of any other examples for each of the categories off-hand...maybe I don't have any