It's honestly not a bad list. Though personally the series has no actually bad games in it, so ranking them is more of a least amazing to most amazing. My own ranking with explanations that no one will read:

XIII - I don't actually dislike the game, so just because it comes last don't think I hate it. But it does have ridiculous pacing issues that put it at the bottom of this list. Though the last fourth of the game would probably rank higher.
III - There is something about three that has always been a bit offputting to me, I find it fun, and I like the job system, but it's just not my favorite.
II - Two is an interesting game, ahead of its time in some respects, but odd in ways that make some hate it. Personally I still enjoy it every time I play it and find the story much more interesting than that of III.
I - The first game in the series and also the first FF I played. I love it for its simplicity and it's sense of adventure.
VIII - This game has some incredible moments, and at its height can be one of the best, but it has issues with pacing (though not as badly as XIII), and with how easy it is to break the battle system. I love Laguna and it has one of the best soundtracks.
IV - A great game for sure, it is only a testament to how good the following games are that it doesn't rank higher. Cecil's transformation into a Paladin is one of the best moments in the series.
V - Best job system in the series, light and adventurous story, endlessly replayable. I do think it drags a bit in the end, but that hardly detracts from an amazing package.
X - Many disagree, but I think X has one of the best storylines in the series. Every character had a struggle and developement, every character had a purpose. The soundtrack blows my mind too. Combine that with my favorite battle system in the series and you have one hell of a game.
VII - I was my first game in the series, VII was my second. Odd? Probably, but man did I love this game, and still do. People say it has aged badly, but truly only in character models and localization. The prerendered backgrounds are gorgeous, the soundtrack is on par with VIII, IX, X and VI, the materia system is smurfing great, only marred by the low difficulty of battles. Cloud's plight is so unexpected and I love every moment of it.
XII - Love it or hate it, XII did some very interesting things with its version of the ATB system. Plus the gambit system is kind of bonkers to this day. Story is great until the very final act and I still enjoyed it. Also has one of my favorite protagonists in the series: Balthier. The setting is absolutely breathtaking most of the time too. Very excited for an HD remaster to come out already!
VI - I have a hard time placing VI. Sometimes I feel down on it, and would rate it much lower. Other times it would be number one. I am not sure what makes this specific game like that for me, but I cannot deny that it is a masterpiece. The huge and likeable cast with purpose and drive. The beautiful soundtrack. What is probably the last challenging battles in the series that aren't superbosses and my favorite last boss fight in the series.
IX - My favorite FF game is the one that I feel embodies what the series represents the most. It is whimsy and adventure and fantasy incarnate. IX is a love letter to the series itself and all of its fans. The fact that this game got a chance to be released still surprises me, after all FFVII and VIII sold incredibly well after changing up the setting and formula, so why would they return to it? But they did and I love it.