Zelda II is awesome! It was really influential to later games in the series. It gave us magic, towns, introduced the concept of different Links and Zeldas and the concept of Ganon's constant resurrection/reincarnation, introduced the story element of the three main characters representing the Triforce with Link being courage, Zelda being wisdom, and Ganon being power, more fleshed out NPCs, bosses like Dark Link and Volvagia, and even the names of OOT sages come from towns in this game.
And I love the mix of RPG leveling/stat building and sidescrolling action-platformer gameplay. Arguably influential to the development of the Metroidvania genre. And I loved the challenge this game threw at you. We really need a new sidescrolling Zelda, even if it's a spinoff.
Ngl, I actually prefer this to the original.