The original Metroid has not aged too well. The world design is not well thought out and has some serious flaws. The lack of a map sucks. Enemies are nothing special. 1 of three bosses is a challenge while the others can be either cheesed or are just easy. Metroid played a huge part in the Metroidvania genre, but has poor design that hasn't aged well just like most NES games.
Final score: 3/10