Some parts are fun hard, but other parts are just annoying. (I'm looking at you, rooms filled with darknuts...) Other parts aren't even hard annoying, just annoying. (Specifically, Death Mountain if you didn't get the Big Key.)
Loosely related note, I'm also on Ganon's Tower in A Link to the Past. The problem is, I'm pretty sure I've used up all my keys and am now softlocked. I technically have a restore point before entering it, but it's also before doing Turtle Rock, and I don't particularly feel like redoing it.
Second loosely related note, while I was doing Turtle Rock the first time, I used a blue potion on the exact frame as I went through a door. For some reason it pulled up the ocarina warp menu. This was really weird because, a. it was in the Dark world, b. it was in a dungeon, c. I was on a blue potion and not the ocarina. I pressed B to exit the menu, forgetting that B selects a warp point, and it dropped me off at Death Mountain's base. In the LIght World. And I was swimming on dry ground. I pulled up the map, but it still said I was in Turtle Rock. When I exited the map... it looked really weird. Think the classic "glitch look" on the entire screen except for Link. (And maybe the UI. I don't completely remember.) At this point, I forgot to take pictures and closed the game, ending the glitch. (Actually, now that I think about it, I made a restore point in an unsuccessful attempt to repeat it.)
Summary: Original Zelda is hard, A Link to the Past Ganon can softlock you, and blue potions and doors don't mix.