Unfortunately since we don't have any permanent quest flags or a way to change exit positions remotely (as this is trying to emulate), you'd basically need a near-complete replica of the entire overworld for every single state of the game. Which means this is as far as something "nonlinear" can get. I doubt what you're working on will have such issues, though.
What else, what else... Oh, if you didn't notice since there aren't any enemies, I used _dojo on the first map (the game ONLY checks the first map's name) but gave you a powerup to immediately overwrite it.
If you use up all the ammo, you go back to the pea shooter as normal, so you can't even tell, but once you get the sword of fortune, you never lose it again when you take damage. Kind of an interesting little loophole there.
You know, this reminds me.... someone DID recreate the entire overworld from the original Legend of Zelda with voxels once.  They also created playable metroid with voxels, and apparently they've done some more things since I've been there last:
If you're gonna recreate the entire overworld, this might be a helpful reference!~
Go ahead. It is highly unlikely that I will progress any further on this myself, and even if I do it will all be in the same undetailed "rough sketch" style as this, and completely linear (all paths unresponsive except for the ones leading to the next dungeon, for instance).
I do like using an 8x8x8 scale for map blocks to keep the screen size matched to Voxatron's, though, and highly recommend it over switching to 256x256 maps.
Hm. I'm sure using bombs to open secret passages would be amazing in here, though. Ha ha.
There is no way for picking up a key in one room to allow you to open a door in another unless that key puts you in a different copy of every room leading up to that door too. :( There's NOTHING to save minor changes in game state except for room number, and because of that it's just entirely better to make much larger changes over a smaller area than it is to make small changes over such a large area to pretend it's being "nonlinear".
Well, probably something will be added to store "changes in game state", as levels (for RPG stuff) or things you can take from one room to another like you can already do with power-ups... it would be interesting to be able to move objects.
I'm too lazy to really make something really complex :P but i should at least try to link together some overworld pieces and see how it works and looks like
Edit: however, adding an "entrance" item would remove at least some of my problems