I think did became popular during it's time because it managed to spawn an anime set on the same Universe.
We won't have the beloved 6 and 7 without 5 giving opening doors for it.
Guys, 5 is fun to play for many reasons.
1. You can customize your team members because of the job system. There are many jobs on this game so you can customize every character to adapt to different fighting styles. You can even give everyone the same job. lets say if you love Mages, make everyone a mage. If you love Ninjas you can make everyone a ninja.
2.Gilgamesh is an interesting villain , he is like Nemisis from Resident evil 3. He wont leave you alone and follow you around.
3. Its the last Final Fantasy Game directed by the series creator.