Metroid is the granddaddy of the whole Metroidvania-genre, and while it’s not the first game that had a large, explorable world in a 2d platformer perspective, it’s the first where all the disparate elements came together into something whole and fitting, where each aspects fed into the next and created one of the best genres we have today.
From adventures Metroid cribbed item-gated progression, though it incorporated them seamlessly into the gameplay (rockets to open various doors, different fire modi to access new areas). From its precursors it took large worlds, but made them continuous and deliberately designed instead of generated on the fly. But the big gamechanger is that as old as Metroid is, it’s one of the earliest games on my Metroidvania-playlist that is actually fun to play, even today.
Sure, there are some elements that makes it less accessible today: after dying your HP-counter doesn’t get refilled much and if you need rockets you have to farm them. This adds difficulty to the game, as farming items from enemies often results in losing more health again.
But it’s the kind of pointless, grindy gameplay that just isn’t fun and only artificially extends the gameplay. The other thing it lacks is a map, which is arguably something you can do without (if your memory is good enough) or do on paper, if you’re so inclined. That said, there’s a LUA-script out there that gives you a modern Metroid-type map and recovers all HP and rockets after respawning, which makes the gameplay experience much smoother.
The LUA-script sadly only works for the NES-version of the game (and hacks of it), not for the one-year earlier (1986) released Famicom Disk System version. That first version had slightly better sound and three save banks (if you want to play it, somebody fan-translated it).
Although, some of the stuff Metroid did was actually quite lenient. Once you get an item, even if you die on the route back, you still have it once you respawn. With that in mind you can plan for one-tour exploration trips without worrying about getting back to spawn points (the elevators between levels). Most of the difficulty of the early game is the lack of any equipment. The only real difficulty spike later on is the Mother Brain and the area before her, which is just incredibly hard.
Overall though, this is it, the transformation point from which on Metroidvania-games or likelike games became actually fun to play.
There are a couple of graphical hacks for Metroid, of which Roidz is my favorite. The art direction is a subtle improvement on the original, making it look as good as some of the late NES-games without being very-in-your-face with the changes. The hack has a tendency to change the layout of the item rooms into small puzzles, which I didn’t appreciate as it broke the atmosphere and took me out of the game (and the whole, find the breakable wall-thing is neither clever nor adds anything to the gameplay). But overall, this is one of the best hacks, and if you then go back to the original it feels drab and lacking visually.