I disagree. I don't think it is underrated either though. I think FFVI is rated - quite rightly - very highly by the fans of the series. The open-ended World of Ruin is a fantastic piece of gameplay that I think is unmatched by any other FF. The music is absolutely phenomenal in places as well.

I do think there is something of an inferiority complex from VI fans regarding its status, manifesting itself in dislike towards other games in the series - particularly but not limited to FFVII - which is embarrassing.