Metroid was a revolutionary masterpiece of it's time and has rightfully earned the title as one of the best NES games.
Let's start with the story: It takes place in an unknown time but definitely in the future. Space travel is now welcome anywhere and the Galactic Federation has been established to provide organized trade, communication, travel, law enforcement, anything the space society needs. The only thing standing in their way are the Space Pirates who want to control everything and destroy anyone against them. A message breaks out among the Galactic Federation that Space Pirates have stole an creature known as Metroid, a greatly feared life-sucking parasite that they plan to multiply by using beta rays. Once that's done, the Space Pirates will be able to come out of hiding and unleash the Metroids on all that oppose them. The Galactic Federation sends a squad of police to their base located on the planet Zebes but they uphold a resistance too strong for them to fight. The Galactic Federation then calls the famous bounty hunter, Samus Aran, to fight the Space Pirates and destory the Metroids. The story is only delivered at the begining and doesn't pick up until the end since it's all gameplay. It's not exactly a problem seeing that this was made back in the '80s.
The graphics are simple 8-bit pixels that aren't anything too special considering it's a retro game and all. The design is a bit strange at times to tell what enemies look like but some are definitely hard to defeat or keep coming back for more. The world of Zebes is a massive maze where you will need to draw yourself a map while playing if you want to succeed. It really does make you feel like a lonely explorer. Powerups are scattered in special rooms and enemies drop health and missles which are weapons mandatory to finish. To name a few of the weapons, there's the normal beam that you start off with but soon upgrade to the Ice beam to freeze the enemies and use them as platforms (My personal favorite) the Morph Ball, which can be found at your left at the begining of the game, to squeeze through tight tunnels and duck. It also invented back-tracking. A new form of side-scrolling which takes you in another direction. Left. It also invented the password system so that every time you'd die it would give a long password to put in at the start menu but it didn't work out to well. It was often glitchy and didn't always accept your password the next time you would turn it off. It was probably the only real fail this game ever really had.
The gameplay is classic gun and run, side-scrolling, exploring, nearly anything goes. The boss fights are very challenging, especially the last one. There are also several different endings making it a starter for speed-running.
The quicker you finish the game, the more Samus will strip for you at the end to show she's a woman. Another new idea.
On top of that, Metroid is must-play for the NES. It's fun, creepy, new for it's time and involves the first woman hero that wasn't a sex symbol.