Zelda II: Adventure of Link is a game for the NES that, while successful for its time, is regarded as the outcast of the series for being different.
The game is based on the same thing as every other Zelda game ever: saving Princess Zelda, who this time has somehow been beaten into a coma. Link has to go to far away cities and lands (like, 8 screens away) to beat monsters and ultimately get the Triforce of Courage and use it as smelling salts for Zelda. Ganon does not make a direct appearance in the game, but if Link dies 3 times, then Ganon is revived...whatever sense that makes.
If you die, you're treated to this image of Ganon...probably of him taking a shit.
There are both overhead and sidescrolling parts to this game. There is an overworld (overhead, of course) where link gets attacked by black people....not actual black people but shadow people. There's also black blobs as well. If you run into any of them, you go into a sidescrolling battle of you vs. some monsters. Once you beat them or run away, you're back in the overworld. On your way, you'll find towns and dungeons as well, which are also sidescrolling. You'll find spells in the towns and items in the dungeons.
You get the usual array of Zelda enemies, and also a few that are only seen in this game. The following includes only the most common enemies and those who are the biggest assholes.
Bits and Bots - Bits (red) and Bots (blue) are basically the most basic enemies - the goombas - of this game. They are colorful boogers that slither at you at the speed of a techtonic plate. Bots are capable of jumping at you, and usually choose to do so right when you're jumping over a hole. There are similar spiky monsters called Myus.
Aches - Cliche bat assholes that swoop at you when you walk by. They are usually called keese in other games, so why the name change? I don't know. The red ones turn into gargoyles (achemen) that spit fire at you.
Mobilns - A Zelda regular, they are the Man-Bulldog-Pig (looks like Al Gore got it wrong) servants of Ganon. They wield spears, and are easy to beat.
Goriyas - While they look nothing like them (in any of the games that they appear in for that matter), Goriyas are supposed to be mustachioed rat men that throw boomerangs. In this game, they look a lot more like Scottish Terriers.
Bago Bagos - These skeleton fish are one of the most annoying enemies in the game. They are easy to beat (always 1 hit), but they spit shit at you and love to knock you into water/lava.
Retards Tinsuits - These idiot wolf men run around aimlessly in dungeons, praying that you'll be stupid enough to just stand there. They deduct experience points from you if they hit you. They hold daggers, but you can not see them here because of the magical white background.
Doomraddles (Mace Throwers) - These guys resemble the red monster guy from the old Bugs Bunny cartoons. They throw maces at you, similarly to how Hammer Brothers do with hammers in the mario games.
Dairas (pronounced by me as "diarrheas") - These maniacal crocodile men run after you either swinging or throwing axes. They are difficult at first until you learn the downward cleave.
Iron Knuckles - God these guys are assholes. If you try to defeat them the way Nintendo intended you to they will piss you off. However, if you jump-slash at their head, you will kill them easy. The Blue ones throw swords at you.
Stalfos and Stalfos Knights - Skeletons that you literally have to hit in their theoretical nuts to defeat. The Stalfos Knights wear armor and are stronger.
Wizzrobes - Klan members that shoot magic at you. You have to know the reflect spell and reflect their magic to defeat them.
Magos - Like Wizzrobes, but they shoot fire and can be killed by swords. They look like the emperor from Star Wars.
Octoroks - Eight legged bags of rocks that either walk towards Link or jump in place. Not much to worry about.
Moas and Girobokkus - Oh my GOD Moas will piss you off. They are eye balls that float around in a quick back and forth pattern. The orange ones will drop fire at you. Girobokkus are much slower, but can close their eye to make themselves invincible. How would a giant eyeball hurt you? Who knows.
Lizalfos - These guys are like Iron Knuckles, but they look like the Gorn from Star Trek. They block better, and wield spears and maces instead of swords.
Firebirds - Only found in the last level, these birds spit fire at you on an arc. They take a lot of hits, so its usually best to just jump over them.
Fokkas (Bird Knights) - The worst normal enemy in the game. One can not ignore that their name is too similar to fuckas. They are like Iron Knuckles, but are faster, can jump, and all throw daggers at you. They take an assload of hits to kill.
These are all of the bosses in the game, in sequential order.
Horsehead - The first boss in the game and rightfully so. This ass backwards centaur just swings a mace at you. All you have to do is jump stab at him and then jump away.
Helmethead - A guy with detachable heads that shoot beams at you. Just hit him in the head by jump stabbing, just like Horsehead.
Rebonack - Basically an iron knuckle on horseback. Just jump on his head and then beat him like a normal iron bitch knuckle.
Carock - It's funnier to call him carrot...or cock. He can be both the hardest and easiest boss in the game. You have to reflect his magic, and if you try to do this in the middle of the room, you'll get your ass kicked. If you duck in the corner though, you'll totally kill this guy.
Gooma - I don't know what he is, but I think he's a Minotaur-caveman thing. He's awful and easy. Jump over his mace and then chop him in the nuts.
Barba - A dragon with a go-go Gadget neck. He's one of the harder bosses, but only because it's easy to fall in the lava. Jump slash his head or downthrust on his head.
Thunderbird - A giant gargoyle with an Indian headdress and wings. You fight him right before Dark Link. He's pretty hard, but just make sure you're leveled up and cast basically all your spells, especially thunder since you need that to start hitting him.
Dark Link - The most poorly drawn character ever and the last boss of this game. If you try to man up and fight him normally, he is hard as balls. However, just like Carock, If you duck in the left corner and just slash a lot, this will confuse the shit out of him and make him walk directly into your sword.
Link depends on magic in this game. You'll learn the following spells by visiting the various towns.
Shield - One of the most important things you learn in the game, albeit the first one. Use it in every boss fight and whenever else you're getting your ass kicked.
Jump - At first you'll find this useful only to jump up on high ledges, but you also need it to be able to hit a few of the bosses.
Life - Your saving grace in this game. Once you learn this, you are set. However, if you even try to progress to even the 2nd palace without it, you'll probably die.
Fire - Makes you shoot fire. Sounds badass, but a waste of magic on the whole. Only use it when fighting enemies that can only be defeated by it.
Fairy - Turns you into a fairy. Sounds gay and useless, and mostly it is. However it is useful for getting up super high ledges and passing screens full of enemies that you're too lazy to fight.
Reflect - Used pretty much only to defeat the Wizard type enemies in this game.
Spell - The most useless magic in this game. It erects (lol) a building out of the ground in one part of the game, but other than that it just turns enemies into bots. However, it doesn't work on ANY of the biggest asshole enemies, and even if you use it the enemies come back if you leave the screen.
Thunder - Basically only in the game to enable you to hit the Thunderbird. It also kills enemies in one hit, except again for the hardest enemies like Fokkas.
The items in this game suck ass. You have none of the classics or anything you can use in combat. No boomerang, hookshot, bow, bombs, stupid ass magical canes...nothing. The candle is the single useful item you get in the game...Link uses it to light dark areas so as to not get his ass kicked. You get a power glove that enables Link to break rocks in dungeons, a hammer that does the exact same thing but in the overworld, a raft that allows you to sail in exactly one spot, and boots that allow you to walk on water (but in one area just like the raft). You'll also get a magical key to open all unlocked doors (conveniently in the last dungeon), a flute that kills a monster blocking your way, and a cross which is sorta necessary because Nintendo pulled a dick move and made a few of the monsters invisible without it. They may has well have said fuck it and not given you any items.
The game is often praised for introducing new elements to the series. For example, it was the first with major non-playable characters and towns. However, this would have probably followed in later games anyway so this is a stupid reason for praise. The game is really challenging until you get the groove of it and level up, so it does offer some play time. It is was listed at 110th in Nintendo Power's top 200 games list. The game also introduced Dark Link, which for some reason many Zelda fanboys tout as the most badass character in the series.
The game is often derided for being too hard. This is not wholly true, it's just that the other Zelda games are very easy in comparison. The key to this game is to level up as soon as you can. However, this does make for some redundant gameplay as you have to beat the same monsters over and over. The save and continue function is ridiculous as well, since unless you're in the last dungeon, both options start you back at the beginning of the game. The worst thing is probably that Link isn't a regular MacGuyver like he is in other games, and does not have a single offensive or defensive weapon other than the regular ol' sword and shield. Overall the game is not bad, but it takes a whole lot of patience and dying.