The first 2 Zelda games despite being very different from one another really felt like they were part of the same universe. They were both awesome. Zelda 2 is my favourite game in the series followed closely by the original one.
In my opinion the basis for the series were very well established by the 2 first games.
We could and should have 2 type of Zelda games for every Nintendo console (home consoles and handhelds).
A 2d version should just expand what was introduced in the very first game: a large world to explore and dungeons full of vicious enemies ( there is a lot more to the game than just that, I know).
Zelda 2 should be the foundation for the 3d ones: Heavily based on combat, very simple to undestand and effective level system, magic, the possibility of learning new moves, freedom to jump whenever you feel like, awesome boss fights, etc. All that with an overworld too, of course.







