I couldn't remember the Minish Cap doing anything interesting with Z but I completely forgot about the floating leaf thing. Also notice how the enemy seems to jump right over Link:
[video width=425 height=344 type=youtube]AMfJM1Acpzo&start=4473[/video]
Also here are some random up/down level transitions, it looks like the ladder had a slightly longer animation then the stairs which has a very short or instant switch.
[video width=425 height=344 type=youtube]AMfJM1Acpzo&start=7345[/video]
That Crusader of Centy clip reminded me that Link's Awakening had a hop item that could jump over pits and gather floating items:
[video width=425 height=344 type=youtube]YzEU19PUVuE&start=2045[/video]
Link to the Past had some puzzles involving dropping between levels at the right spot:
[video width=425 height=344 type=youtube]i9e9jGF6JrM&start=1768[/video]
And also had this system of two levels on one screen (with things not interacting between them):
[video width=425 height=344 type=youtube]NKNDzLfzAzs&start=816[/video]
I don't think Seiken Densetsu treated different Z levels in any particular/special way. From my memory basically all the entities were on the same 2D grid and height differences were illusions of the background only. See how the players attack enemies on different levels here:
[video width=425 height=344 type=youtube]g7T7N098RJo&start=6960[/video]
[video width=425 height=344 type=youtube]d7Co0GX7jI4&start=7701[/video]
Landstalker and Bastion are sort of a different category all together. This type of view is usually called isometric, though I've also seen this particular flavor of perspective called a dimetric projection
since the camera angle to the ground is not 45° (usually something closer to but not exactly 30°
to make the tile size 2x1).
You can get some neat z-level stuff going with this kind of perspective, but it does sort of feel like a bit of a different direction then HH is currently going... Maybe there's still some things we can learn from how they handle things.
One of my favorites in this style is Mario RPG. By comparison I have trouble reading Landstalker at times because there's no player shadow there!
[video width=425 height=344 type=youtube]hbyNog7o1TE&start=155[/video]
I believe Casey has expressed some valid concerns about the readability of floating things and telling when things will collide. I think at one point he used Zelda 1 and Binding of Isaac as examples... In the former, there's no ambiguity: when the arrow touches an enemy, it's a hit. In the latter it's not so clear: what about when both the enemy and the projectile are in the air? At different heights?
If the player is jumping this is even worse: can the player jump up to attack things that are further up in the level in Y? If I'm jumping will I be hit by projectiles where my player sprite is, or where my shadow is, or neither, or both, or does it depend on how high I am and how high the projectile is?
There's a number of issues! (Last I remember it sounded like Casey wasn't planning on having jumping? Maybe for some of these reasons?)
Another interesting question is how/if things will be able to move from one Z level to another. Will they fall in? Will some enemies be able to fly up through holes to other levels? What will that look like in the level they are leaving? Dunno what Casey's plans are, just letting some ideas flow around.. I'm looking forward to seeing how things develop.