The Beginning of The Game
The story of Zelda II starts like the game before it, with an intro story scroll.
"After Ganon was destroyed, Impa told Link a sleeping spell was cast on Princess Zelda. She will wake only with the power of No. 3 Triforce sealed in a palace in Hyrule. To break the seal, crystals must be placed in statues in 6 well guarded palaces. Link set out on his most Adventuresome quest yet..."
Well since Adventure is in the title of the game I suppose this could be his most adventuresome quest yet. It's also funny to see that Link is placing crystals in statues as the goal because in the next game in the series Link to the Past the goal is to collect the crystals... err pendants... err... sage crystals!
I also like that there is some ambiguity on who cast a sleeping spell on Zelda. But that ambiguity lasts all of a handful of minutes because when all your lives are gone a red screen flashes showing an outline of Ganon with him laughing at you harkening his return to Hyrule. Yeah I kinda figured it was him but Zelda II is a sidescroller so it's possible they changed other elements and I just didn't know about it.
You're Going To Die A Lot
The original NES Legend of Zelda never felt too difficult to me. Whenever I played the game I had a map that a friend made me or something I made myself. The difficulty of the dungeons never felt too crazy and the last dungeon wasn't too hard... if you mapped out your route. I personally never played the second quest but the first quest always seemed amazingly fun and not too hard. I felt similarly about Link to the Past and Link's Awakening. Come to think of it i've never felt any of the Zelda games were too difficult. Sometimes what you have to do next was impossible to figure out and I had to ask a friend or consult a player guide but I've never considered the games to be particularly challenging. All that said Zelda II: The Adventure of Link might be the most difficult Zelda i've ever played.
Zelda II has a experience based progression system that when you gain enough experience you can level up. Health, attack and magic are all abilities you can level up and each makes you tougher, hit harder or the ability to use less magic while casting spells. Along the way you can find heat containers that increase your life and magic bottles that increase your magic. To progress through Zelda II you need to make sure you are collecting enough experience to level up while making sure you get each heart and magic bottle or else the game will simply be too difficult. For instance, after you complete the first dungeon you can either go south to get the hammer or east for the second dungeon. I opted to go for the hammer so I could make my way easier through the overworld and I spent over 10 runs and 6 level-ups before I could make my way to actually collect the hammer in the cave maze. I might have taken that part a bit early but I was also getting completely wrecked at the second dungeon too. Zelda II is a fun game but it's the first Zelda game i've spent time level grinding to progress.
Zelda II Is All About Defense & Run Management
Zelda II reminds me of a modern rogue-like in that each enemy has a specific method of attack and way you approach it and if you don't consider defense to be more important you will not progress through the game. In fact, i'd say a good defense coupled with health management is the most important part of Zelda II. In most games you can ignore small enemies that you outclassed because the amount of damage done to you is minuscule and you can easily heal. It's the same in Zelda II as low class enemies don't do much damage to you but healing is hard to come by and you need to plan your run accordingly. For instance the best healing in the game is a spell you get but that takes up magic which isn't easy to come by either and you need that magic for defense and jump spells. If you run out of magic and you need the jump spell you can't progress. If you run out of magic and you need the defense spell for a tough run of enemies you will die. If you die too much the game is over and you can continue but back at the start of the game.
Zelda II is a game all about managing your runs to dungeons, items and the like and how to balance when to focus on leveling up VS when to focus on getting items to progress. For instance if I am close to death on my last life but also close to leveling up I'll choose leveling up and focus less on progression so I can save the game and restart my run. But if i'm close to collecting an item (key, heart, hammer) I might choose to avoid fights to collect the item so I can die, save the game and start over a new run.
I'm using a map to make my playthrough of Zelda II easier and I'd recommend you do the same if you are going to play it. Like nearly all the NES games i've played recently on the classic I am using the map out of the Playing with Power book. The Zelda II maps aren't perfect and contain a few omissions like they print out the general area where you can find Bagu but not the actual tile location. Some of the text is also vague but I didn't find it too hard to figure out or enhance it with a quick search online.
If you missed out on Zelda II and are looking for a challenge you might want to play Breath of the Wild. But if you played that and want to head back to something a bit more retro, Zelda II is here and Ganon is ready to laugh at you each time you die.