Severely overhated, in my opinion (taking later releases into account that is, the NES/Famicom version still sucks). I am one of FFII's biggest defenders.
The gameplay does suck for sure, however, I don't think it's quite as bad as people make it out. Again the Famicom version is just kind of bad but other versions are whatever.
The story, while absolutely nothing amazing, has a lot of ambition behind it and is ahead of its time in every sense of the word. Not very complex, but it is legitimately trying to convey some character work and themes here and it's really cool to see that in what would later become a very story focused series.
Great music too. Rebel Army my beloved.