To the poster above- Heresy I say! The original Metroid is a master piece! Sure in some ways it's dated but the design/exploration and atmosphere/music still hold up.
It's not "in some ways dated", it's massively dated in almost every way. The design/exploration don't hold up at all - it's an absolute nightmare to navigate that horrible mess of a world without a map, especially when most rooms are identical except for the occasional random hidden block you can bomb to get through to... another copy-paste room, most of the time. The atmosphere maybe holds up, okay, but I wouldn't say the music does, honestly. There are a few good songs in the game (Title and Kraid, mostly), but also some terrible ones (Ridley and Tourian), and I've never been a big fan of the classic Brinstar theme (from a compositional point of view, it's so simple and barebones it hurts). It's not the game's worst aspect, but it pales in comparison to almost every other Metroid soundtrack in my opinion, and I'm glad its composer never returned for future games - his style just didn't fit the series.
The worst part is definitely the difficulty, though - not because it's hard, but because it's unbelievably, unacceptably cheap. Starting with 30 health regardless of how many energy tanks you have is stupid enough, and then made worse by how insanely long it takes to farm for energy, often resulting in farming sessions that can take upwards of 15 minutes every god damn time you die just to get to full health again - never mind having to travel all the way back to where you were before dying, through that confusing mess of a map. Then there's stuff like getting hit by enemies as you go through doors (this is even unavoidable on one specific door!), not being able to hit any small enemies without using bombs (which isn't necessarily hard, but it's unbearably inconvenient), or getting stuck in acid until you die because you couldn't tell which was the fake acid between two identical looking rooms. And don't get me started on the bosses... Ridley is a piece of cake, but a terribly designed one; but Kraid and Mother Brain, well, if you don't know exactly what you should be doing from the first second and do everything perfectly, you're basically guaranteed to die within seconds. And then get respawned halfway across the map, with 30 health. Lol. Yeah, I'm never playing that crap again, thank you.
It's great how much it innovated for its time, but looking back and knowing Castlevania released on the very same year, it just puts in perspective how cheap games like Metroid were even back then.
In other topics, I really should get playing those GBA Castlevania games.