Overall: 8.4
   Metroid is a fun and addicting adventure / shooter game from the late 80's published by Nintendo. you venture through a distant planet collecting new items and killing enemies.
Graphics: 7
   As far as 8-bit NES graphics go, Metroid has great graphics that really set the dark atmosphere. the  landscape is very detailed as well as the enemies. though sometime you do get tired of looking at that blank space in the background.
Sound: 7
      Nintendo NES wasn't known for great sound capabilities. Those loud or scratchy beeps can be a pain to hear sometimes. Apart from that, the music is wonderful, catchy, and set the dark tone that Metroid is supposed to make.
Addictiveness: 9
         Metroid is very fun and addicting because you are always exploring new places, earning new power-ups, and fighting new enemies. you are never disappointed. you might find yourself playing this for hours, continuously, getting stronger and defeating the 3 bosses.
Story: 7
       If waiting at the title screen the story will appear. your character, Samus aran, is supposed to venture through planet zebeth to fight the space pirates who are holding the metroids captive. you deafeat, kraid and ridley, and their great leader, mother brain. there is not much effort put into it but still, it has a story.
Depth: 10
      Metroid might just be the longest game up to its time. you explore the caverns of the humongous plantet zebeth. the game is separated into five worlds: brinstar, the blue rocky world, norfair, the fiery world, kraids base, ridleys base, and tourian, the main space pirate base. you collect about 10 powerups, not including the dozens of missile or life expansions. again, LONGEST GAME up to its time.
Difficulty: 8
    Metroid ranks high in difficulty.Enemies that fly at you, drop from the ceiling, or have lots of health can be a pain to kill. it is mandatory to be careful not to fall in to the lava pits or they will take a huge chunk of your health. it also sucks that you only start with 30 health (out of 100).

Metroid is a pretty good classic. I've played this for quite some time and had plenty of in game accomplishments. Quite a classic.

I have heard many good things about this game... I tried to play it once, But I couldn't go very far because I didn't knew what to do or where I should go...

However, excellent review!

Metroid is one of my favorite Games on the NES. The music is GREAT especially for a game that came out near launch. The controls and powerups are AWESOME, and the game was just huge for it's time, as you mentioned.

Good review, although I would work on your spacing a little bit. A space between paragraphs, or bolding would really help.