From my experiences, 7 was by far the worst FF game in the lot. (That said, I haven't played all of them. 4,5,6,7,8,9,10,12,13, and the whole tactics franchise)
Sephiroth is an absolutely terrible villain. The expanded FF7 universe starts to do him justice, but his whole premise is "He's a really bad guy! With a really big sword!" I'd say he's evil because he's crazy, but that's an insult to Kefka. Sephiroth is evil because he wants to blow up the world because... reasons..? Compare him to Jecht/Sin, who actually ends up being the hero in the long run because he set you up to break the cycle. Or Kuja who is the hero for the other side, who lost his position to you, then tries to regain his position by completing his mission and trumping you, his replacement? Kuja isn't a bad guy, he's just imperfect at what he's supposed to be doing. That's deep. I would love someone to actually explain, based on the original game only, what makes Sephiroth so great.
Cloud is a boring main character. "He's the good guy! With a really big sword!" Doesn't go much further than that. Oh, and he spends a whole disc of the game in a wheelchair on some island because he can't handle the fact that there's a rainbow.
Tifa has boobs... and can't remember her boyfriend, because he was dropped at the last minute of production in favor of Cloud, from my understanding.
Barrett is a black guy with a gun. (Who lost his daughter, a point that is brought up a couple times and should be core to his character, but they really don't do much with him after the first hour or so of gameplay.)
Aerith is a really big deal because we're told she is. Also, she died! Oh no! She has next to no personality except that she picks flowers.
Vincent is dark and brooding and a vampire! Honestly, later games do him incredible justice. But the original game make's him a huge cliche.
Yuffie is a valley girl ninja. Well, at least that one's not a cliche.
The most interesting characters are Cid, who sounds like he has an awesome past but they never really go too far into him, and Cait Sith, who is actually incredibly well written (An animatronic cat piloted by a guy who is fighting against the evil corporation from the inside, and is trying to keep his efforts hidden? That's actually cool!) but no one uses him because RNG, you get him really late, and they just don't do much with him. Red is pretty neat, but doesn't really add much to the world. The game wouldn't be much different without him, and he doesn't leave that much room to expand.
So the characters suck, and the more interesting ones get zero attention.
The story itself leaves so much room to be awesome (ignoring the terrible villain), but falls short due to poor choices.
The music is fucking fantastic. The Materia system blows some other systems (namely the Draw system...) out of the water, but isn't the best (I personally prefer the Sphere Grid). The world itself is interesting enough, I guess. And yes, it was in 3D.
Admittedly the first hour or so of gameplay (the actual reactor raid) is quite neat. Also there are definitely some awesome moments (The date on the Golden Saucer, "I'll SMASH EM," and a few others).
Honestly, I couldn't beat the game until I swapped to a DDR pad to play it. I played discs 2-4 just with my feet because I had to keep my blood flowing or I would have fallen asleep. I wanted to beat the game to see it all through, but my god was that hard.
I realize I'm being quite hard on the game, but if you compare it to 4, or 9, or 10... how is this the popular one? Fuck, I enjoyed 13 a hell of a lot more up until chapter 11 where it opened up and got grindy.