I will fully admit that I didn't grow up with an NES, that I'm a casual who reads VNs and plays match-3 for fun, etc. But I did complete a couple of NES games on, uhh, alternative hardware, and Zelda 1 was one of them, and I did beat it. So I am familiar with the game itself, and I don't have anything against the art, audio and other visual aspects of Yancy - in fact, I think they are the best features of the game. The game looks REALLY good, and the way sprites move and the map transitions animate feels faithful, I didn't have any trouble with it. Maybe they are just a tiny bit smooth, to be AUTHENTIC, but who cares. They work fine and they get the job done.
However I did have trouble playing the game. There are 3 main issues I have.
1) No invulnerability frames. This one is pretty simple to explain - you get hit - you don't have any time to recover or regroup. Very noticeable for the "Fist and head" boss in the research dungeon where the head spews a chain of fireballs side by side. If you get caught up in it - it's over. And this would've been fine, I can understand the lack of i-frames if the answer would be "git gud", but...
2) Not all enemies telegraph their attacks. Specifically the octorock-likes to the right of the first screen, same with blobs shooting arc balls. They attack the moment they stop. And if their placement is extra dickish (like the right screen from the spawn) - it just kills the fun when you can't consistently pass through a second screen of the game. Yet other enemies - like the skeletons, or the rock floating heads in the research dungeon - have no problems telegraphing their attack, and thus being WAY easier to deal with. Longer sword doesn't help - in fact, in my experience it was way easier to get screwed over by the octorock-likes because it takes more time to attack.
The placement seems very intentional, and unless I'm supposed to learn the time of cooldown of the octorock-like attack - I don't see a way to reliably kill them without taking damage - attacking one from behind the rock leaves you exposed to the attacks of the other one. I cannot fathom a way to reliably kill them in a reasonable time. (reasonable = short, since I consider these octorock-likes trash mobs due to them being so early in the game)
3) And lastly - the only way of not getting hurt by the projectile is running away. It's tough, since you get locked in once you attack. Zelda avoided this problem by giving you a shield that blocks projectiles if you're facing the projectile and not attacking. Without it the second screen to the right becomes, in my opinion, too hard to reliably pass through without taking damage.
I get the feeling that you want to make "harder" zelda, which is fine. But it's just too hard for me, especially if it's like that from the get-go. There seems to be close to zero foreplay. Again, it's fine for mobs that do telegraph their attacks, but when they don't - it feels like the only way to figure out the way to progress is to bash your head against the wall until one or the other cracks open. Potion is an invaluable addition due to the lack of i-frames, but at the same time - I would like to save it for bosses, not for trash mobs next to the first screen of the game.
Sorry, but getting killed over and over again is not fun for me, especially to trash mobs. The difficulty spike is just too big.
Two other notes:
1) Skeleton projectile passed through the rocks. Dunno if it's a bug, but it feels inconsistent with other projectiles. I expect to be able to hide behind a rock from a projectile, especially since I don't have any other means of blocking them.
2) Your game seems to try and resize itself to size 0,0. I had a daemon running that unblocks resizing for games, and your game immediately shrank itself until I found out the issue and killed a resize unblock daemon.