Nomenclature
The Dark World that the Temple of Light leads into is going to follow the lore of the Sacred Realm as told in LttP and OoT. Essentially, this means that:
1) The Sacred Realm mirrors most of the terrain in Hyrule, but modified as per the next point.
2) The Sacred Realm also mirrors the "heart" of the holder of the Triforce. A balanced heart will make the Sacred Realm into a greater, more paradisal version of Hyrule. A heart in turmoil will make the Sacred Realm into a fearful, monstrous version of Hyrule.

However: in this game, Lord Menace does not possess the Triforce! (Even attempting to do so would utterly destroy him, as he is composed of primal Chaos and the Triforce is the symbol of divine Order.)
But, he has used his chaotic influence to seal, or neutralise, each individual Triforce's power - with the result that nobody can "hold" the Triforce until the seal is broken.

So, the "Dark World" isn't "dark" because it mirrors the heart of the holder. Instead, it is dark because of Lord Menace's chaotic, corrupting influence upon the world itself.

Up to this point we've been referring to it as the Dark World, but doing so implies that it is of the same nature as LttP's Dark World. Thus, I propose that we henceforth refer to it as either the "Chaos World" (referring to the reason why the world has become inhospitable) or the "Mirror World" (a very fitting name which NeoFirst's NPCs will refer to the not-necessarily corrupted Dark World as.)

Transformation
There is a third rule concerning the Sacred Realm which I didn't mention:
3) Whoever enters the Sacred Realm will be transformed to mirror the state of their heart. A virtuous heart will transform one into a wondrous being. A vicious heart will transform one into a monstrous being.

This is something which is easily forgotten. When our heroes Link and Zelda stride into the Temple of Shadows, they will be changed into different creatures. In LttP, such a change prevented Link from using any items, but I don't think that NeoFirst needs to follow that particular trend - NeoFirst's Link and Zelda aren't quite like their LttP counterparts.

Alternatively, we could wimp out and just drop in some Moon Pearls (the only item which can overrule the effect) for the both of them.

Some other notes:
* In reference to the "Mirror World" name, and also to LttP's Magic Mirror, all entrances to and from the Chaos World will resemble mirrors.
* I understand that Silver Arrows are required to activate the Light->Chaos mirrors, and that Golden (Triforce) Arrows are required to activate the Chaos->Light mirrors.