I have never been a proponent of Zelda II. While I do not think that it is a terrible game, it has certain qualities in its design that leave a lot to be desired. Many gamers tend to enjoy the platforming elements of Adventure of Link, but the RPG elements are too dominating.
First of all, the Zelda series collectively has never been about solely killing enemies to become stronger.The emphasis has always been upon the journey and the collective experience that Link draws his strength from. Farming for experience points in Zelda II was boring and zapped the fun out of the game.
The lives system added difficulty, but not pure difficulty that comes from the quests in the game being particularly hard to overcome. It wasn't just the fact that enemies were not that easy to defeat, but it was that in the midst of farming or even going through a dungeon, your whole bevy of accomplishments could be wiped away.
Certain annoying elements of game play such as not being able to accurately jump, meant that you had to waste your jump magic just to clear an ordinary lava pit, or if you are touched by an enemy Link automatically jumps backwards which would mean that you fall into that lava pit.
Don't get me wrong, I've enjoyed playing Zelda II. Beyond its annoyances is solid game play and a unique excursion throughout Hyrule is well worth the time it takes to play it all the way through.