FFV is my favorite 2d entry.
It is not a lighthearted game. It's tone is more versatile whereas FFIV &FFVI are more one-dimensional. Two of the characters' dead father visits them in a ship graveyard early on in the game. Shortly after that Galuf recalls how he sealed a dude away while he begged for his life, to the tune of X-Death's Theme, which is one of Uematsu's most haunting melodies. A character you spend 20+ hours with dies. Entire regions are ripped from the planet and Reina's backstory with her mother and her dragon is one of the darkest back stories in a FF game. But FFV also claims some of the funniest and most charming moments in the series and that's why I prefer it to the more popular games surrounding it that western gamers got to play during the impressionability of their youth. It also happens to be the only game in the series with balanced gameplay and properly progressing enemy challenge.
Every game in the series can have the merits of its plot knocked down fairly easily. FF has never been about the story per se, the themes a player is supposed to take away, rather FF is about the memorability of the moments. FFIV starts off with a bigger bang but it doesn't stay as enjoyable throughout. You meet a new character, someone they love dies, they help you get something, and you get betrayed for the item. FFV is more intricate. FFVI is another matter. It had the beginnings of a revolution in gaming glowing through the cracks but it doesn't have the balance FFV does or the versatile moods, which is why I prefer the games surrounding it over FFVI.