I totally agree with Whitay. Basically, the overworld wasn't interesting and towns had practically zero depth as well, which isn't a surprise for a NES title, having limited resources. Adding some real content to these areas would help a lot. It would be interesting to see the overworld converted into the normal style for 2D Zelda games, where you don't have a zoomed out version. That said, it would be a pretty big amount of work if you wanted to do it right.
I personally like Zelda 2 because of its difficulty, and many games today are just too easy. I think a lot of people might say they like easy games, but in many cases, I expect it's only because they didn't give harder ones a real chance. When a game is too easy, it's just not very rewarding/fun to play it. There are ways to design a game to be fair while making it challenging at the same time. Just be careful. If it gets too easy, the game becomes far less satisfying to many players. If it's too hard and unfair, players will just get frustrated. The key is to make it challenging, but use hints intelligently (the best hints are the hints that make the player think they figured something out on their own) and save points of some kind to give players a chance to learn how to overcome difficult areas, to learn enemy patterns, etc.