I dont know if theses suggestions already been post, but oh well
1. It would be nice to change the annoying screaming sound when Link random scene encounter when walking on overworld to something more soft like the original japanese version.
2. For lower HP blue guy in the great palace, I completely disagree, it is supposed to be hard and we just need to learn the pattern of each monster to beat them.
3. shadow link weakness should be removed (staying on left screen and keeping slay) that is a trick on US version.
4. replace the blue knight mini-boss before the fake wall in the 5th palace by the boss in the 2nd palace (keeping the final boss from the usa version)
5. Add couple of towns without nothing special and 1-2 palaces without crystal, just to make XP
6. when we use shield, the effect doesn't disappear when we change scene.
7. raft should have a second utility instead of just 1 time, dont know what what it could be.
8. the long bridge to the maze island should have couple of fight scenes.
9. It would be nice to have a sword upgrade like in Zelda 1. I know we can upgrade sword with level up, but it could be nice to have both. Lets say you are at level 4 for sword, if you find the second sword, it it hit harder at the same level .. I would put that sword somewhere in a forest on second world, protected by hard monsters or in a palace (if the palace is closed before getting the sword, too bad lol)
Or maybe a shield upgrade that help link take less damage ?
10. replace the magic key with another useful item ? the magic key is some kind useless in my opinion..