Update: That age of darkness I mention in the paragraph below has come to pass: Nintendo has killed a clever tribute (opens in new tab) to one of its best-loved games. Sadly, Zelda30Tribute is no longer playable.
The remaining dungeons and the accompanying overworld are to follow, in addition to major bugfixes. Boomerangs, for example, are completely broken, while that chippy warning bleep you get when on your last half-heart of health never turns off. As the devs put it, "This is not the greatest game in the world, no; This is just a tribute."
They're not the first team to experiment with voxels in your browser—there's a functional NES emulator (opens in new tab) that extrapolates 3D models from sprites in any ROM you care to feed it.