Zelda two was more of an RPG, with a top down overworld. Monsters appeared on screen and attacked you, just like in Mario RPGs, except that they were nearly ikmpossible to dodge. When you fight, or enter a dungeon or town, the game switches to side-scrolling mode, in which you fight real time castlevainia-like battles against pixelated baddies.
It was difficult. Much harder than ALttP, so hard as to be frustrating, as most games were then.
To make it worse, you had to start back at the beginning with every game-over. Which is why I never finished it.