Why 7 as number 1? Rare to see someone praising 7 as the best in the series if not for nostalgia reasons.
Gameplay, locations, soundtrack. Hating on 7 became a dumb meme because of how ridiculously popular the game is, while 6 is more niche (and incredible, but 7 is great too).
It has the best gameplay out of the blobbery turn-based games, especially if you use the FF7 Hardtype mod. disclaimer: my ranking is influenced by said mod, though it only touches difficulty and balancing and is faithful. FF7 has the incredible materia system (the mod's increased difficulty makes strategy and diff. materia combinations more meaningful, and nerfs some shit. Combat is much better as a result), fun mini-games and puzzles, take for example the coupon puzzle in the Shinra building, the Icicles in Gaea caves and then the timing challenge in the north crater immediately after with the wind, stuff like that, devs constantly throwing fun at you with arguably better execution than others in the series. And how did I forget shortly before the Gaea caves you're doing a fucking snowboarding mini game because why not! ...tbh that part ain't that great because it is rather disconnected from the rest of the gameplay/world. Usually puzzles and mini games reward combat items at least, this doesn't.
...further still, in the one area between the snowboarding and Gaea caves there is something like
5 more fucking puzzles or mini games I was forgetting: The traditional
leap frog puzzle. The initial mountain climb where you have to keep your body temperature up (not a great mini game). The snow field where the camera rotation fucks about with your orientation. And finally the navigation of the whole Great Glacier area being a timing and orienteering puzzle in itself, where have to figure out the map and you pass out if you hang around for too long. All the while you're messing around with materia builds, fighting challenging enemies (with the mod), nabbing those enemy skills etc.
As an another example, note the layout of an area in the North caves:
They weren't afraid of shit not making any realistic sense at all for the sake of gamey fun. This is the case for all the classic FFs, but it is peak here.
Or! how about the temple of the ancients? The huge maze, then the random boulders, then the best part, the keeper of time:
Exploration is p. decent in the game too. It's a somewhat linear game like the rest but there's just enough exploration to satisfy.
There's plenty decent gameplay design in all the classic FF games starting with 5 and ending with 12, but in 7 + Hardtype mod holy shit is it fun as hell. I'd say 9/10 gameplay while before it was like 7.5/10 maybe 8, which would be the highest rank I'd give to any game in the series, and any turn-based JRPG I've played.
That's enough gameplay talk (though this is the type of stuff fans of overhyped garbage like Chrono Trigger and FF4 just cannot really grasp. Such boring-ass gameplay).
The art style while the characters look like absolute ass and create inconsistency, backgrounds are just incredible. And said janky models have tons of charming animations. The variety of locales is so cool too, from cyberpunk dystopia to chilling on a spanish-inspired beach resort?
The soundtrack is of course great, but that is the case for most, naturally.
Story is batshit insane but it has plenty charm nonetheless, aside from Cloud's story in Kalm and his "finding [of] himself" in the lifestream. God I hate those bits. But yeah, that whole subplot with Don Corneo wanting to fuck every woman he sees culminating in you teaming up with the Turks in Wutai and whatnot, just hilarious. Plenty of great moments even if the story as a whole is campy and inconsistent.
6 used to be my favourite with 7 coming in probably second, but I went back to them all recently after nearly a decade and 7 was a shitton of fun. The FF7 Hardtype mod I mentioned had a big hand in that though as with it the gameplay shines twice as bright. Highly recommended!
I played a shitload of games last year and FF7 + mod was definitely one of the most memorable. The Square Enix remake is going to butcher the hell out of a classic. Those cunts destroy everything they touch.