Have you not played the original LoZ before @stigzler? If you haven't, you should redress this issue immediately! The nostalgia goggles are in full effect here, but even after all these years, the first title in the series is still my favorite. I go back to it time and time again. To my mind it is a perfect crystalline example of zen and the art of gaming, lol.
At any rate, I was able to make it to the first dungeon in this browser version. No idea whether all the dungeons have been implemented (heh, I'm at work right now), but it does seem like a 1:1 representation of the original game from what little I've seen.
Pro Tip: Your first order of business should be to enter the cave you see on the very first screen. It's dangerous to go alone don't 'cha know!