Final Fantasy is one of the game series started in the 80's that suffers from so called Curse of the Second Installment where the second game of the series is weaker than others (other examples from these game series are Super Mario and Legend of Zelda). It's usually because developers try something new after their best-seller.
Story in Final Fantasy II is anything but new. Rebellion's fight against evil empire of Paramekia (or Palamecia, who knows) feels too much taken from Star Wars. There is Luke Skywalker-clone, Darth Vader-clone, Emperor-clone, even Deathstar-clone. Characters are not personalities, bad guys has no clear motives. It's also annoys that too many characters are so eager to sacrifice themselves.
The new part in the game is an unique system where is no experience points or levels. All skills are developed how often they are used, for example magics become more powerful. There is a good reason why this system has stayed unique. Developing any other than attack power is very slow so most of the magics won't receive their fullest potential before the game is over unless players develop their characters day and night. It's not a problem because dungeons are once again too large and of course, without save points.
Game's atmosphere is the reason why there are more than two Final Fantasies. Nobuo Uematsu's music is good, specially world map music is beautiful and makes forget for short time that's it's only 8-bit voice. Also monsters are mostly own design and they are mostly not ripped from Greek mythology or AD&D universe. Only die-hard fans and nostalgics should try this, for others it's not worth of it because of it's clumsiness.