Adventure of Link was a Zelda game that made a very different turn from the usual way it's done. I find the game itself to greatly resemble the game, Castlevania, but that's beside the point.
The original Legend of Zelda, and the Adventure of Link both lacked any puzzles other than "kill all enemies in the room and the door opens." To compensate for that, they made monsters much harder. However, Adventure to Link was easily the harder of the two. Link seemed to have a smaller reach in that game, so it was required to get up in the monsters' faces to do any damage. But at that length they can deal out serious damage to you too. Monsters generally had a much harder killing scheme to them as well compared to most other enemies - especially in the beginning. The difficulty of some monsters in the first palace were far greater than the ReDeads in the Shadow Temple in Ocarina of Time - at least in my opinion.
Overall, the game was quite tough, but it got noticeably easier with great skill - and sometimes luck.