the fact that you basically have to read the manual
This is no joke and deserves a bit of emphasis. NES games expect you to read the manual.
I did my first play of Zelda 2 about 5 years ago. I didn't like it as kid, but I loved my adult playthrough. I will note that this was one of the games that I got stuck until I read the manual.
Another Z2 pointer, to anyone that wants to give it a go, is that you can logically "soft lock" the game with bad key management. It's unlikely, but if you like to look for unintended orders to do game goals, it could happen.