Games not under consideration:
Final Fantasy II
Final Fantasy III
Final Fantasy VIII
Pretty simple, I can't rate what I haven't played.
Games really not under consideration:
Final Fantasy XI
I don't mind the fact that square decided to develop a FF themed MMORPG. I do mind that they gave it a numbering in the core progression. This is something that should have been spun off as a side property, like Tactics or Crystal Chronicles.
And with out further ado:
Final Fantasy V
I haven't finished V, but I've played enough to know that it simply isn't worth the retro trip. While the game did introduce game design concepts that would be put to good use later(the job system, specifically), it wasn't implemented very well and the story and characters were just a pile of dumb cliches and most of the game is boring grind. What's really remarkable is that this is the game that was sandwiched between two better games, and doesn't seem related to either of them in almost any way.
Yup, it's the granddaddy that launched everything else, and ought to be given some credit for that, right? Well, keep in mind that this isn't a list of "most influential", but rather the games that I think are best overall, and a large part of that is fun. And given this games lack of much story and slow, plodding gameplay style compared to the later entries, I just don't think it stands up. It's a prototype, and most prototypes just don't perform on the level of later refined models.
Final Fantasy IV
This game was a significant step up, and there are actual characters that come and go from the party throughout the story. The problem I have with this one is that I didn't play it until several years after its release, after I had not only played a later Final Fantasy, but also a number of other RPG series that either borrowed heavily from, or were enough similar to, FF IV that I have a hard time remembering it as anything special. So, I enjoyed it, but I'm unlikely to want to play it again.
Final Fantasy IX
This game is a lot of up, and a lot of down. I like the general sense of the world, and it's too bad this wasn't a later release: better graphics would have helped dramatically in many places. I also like that many locations, specifically the cities, change significantly over time as various events happen in the course of the game.
On the other hand...
Let's start with the characters. Most of them are caricatures of people, and I'm not talking about the artistic style. Only Vivi, Freya, and Eiko showing any depth of emotion or true conflict during the story. Most of the others are really shallow, and Quina wins the distinction for being the most annoying/unlikable party member in the entire series. Zidane is a "party leader" type basically in the "Chrono" class: He is stronger and faster than the other characters, and his trance is vastly stronger than anyone else's. None of that is very pleasing.
Speaking of trancing, that was a mechanic that didn't work. Since you don't really have control over when it will happen, there are going to be a number of times where you get it activated right before the last monster dies, which is frustrating. All in all, not a bad game...but not good, either.
Final Fantasy XII
A pretty game, to be sure, and there are a lot of wonderful details, like the bestiary, to show they put lots of work into fleshing out the details of the world. There are some good twists, including the first time Dr. Cid has actually been a villain.
That said, most of the plot revolves around the character Ashe, as she travels the land whining at various political power players trying to get her small kingdom back. While she does eventually make a heroic decision, that happens later on and doesn't retroactively make me think she has a good claim to actually rule her hereditary land.
A sticking point for me is that FFXII says it is set in Ivalice, a world that was first used in Final Fantasy Tactics, a game I absolutely love. The reason this is a sticking point is that the Ivalice of XII bears no resemblance to the one from Tactics. Well, XII tries to ape FFT's political drama, but falls on it's face where Tactics succeeded gracefully.
A big issue for me with XII was the combat. It was frankly boring having to watch characters saunter around in real time while they had to wait for their action bars to refill. Also, there always seemed to be a substantial delay between me telling the game to do something and it doing it, even with a full action bar. This got really aggravating at times, especially when I needed to heal immediately.
Actually, I think I'm less likely to replay this one than IX. While XII was consistently better, the highlights of the IX story are much better than that of the XII story.
All of the rest are good games, but it's late and I'm tired, so I won't say as much about them.
Final Fantasy VII
Yes, it's good. It's just not as good as most people seem to think. Edit: The combat is generally good, and the plot has some good twists and a well-designed villain (I mean Jenova). That's some of the good stuff. As for the bad stuff, it's really tempting to say "the cast" and leave it at that: while I can't remember all of the details of the plot, I do remember having a strong dislike for Barrett, Cait Sith, and especially Yuffie. Oh! Though one thing I do have to mention is how much Midgar's existence threatens my suspension of disbelief. One city, which for absolutely no explained reason holds most of the world's population? No thank you, things don't work like that, which the plot basically demonstrates.
Final Fantasy XIII
I haven't finished this one yet, but if things continue without getting better or worse it is looking at at least this spot. The story is excellent, every one of the main characters that have explained themselves so far act like real people, and the combat flows nicely. It is a game that has taken a lot of good pieces from previous Square games and put them together to create something excellent.
Final Fantasy X
While I'm not exactly a Tidus fan, most of the characters are very good, and even better, the world they live in might be the best Final Fantasy setting so far. Except for the odd details of Yu Yevon, why Spira is the way it is makes sense, and is thematically consistent and provides a great framework for the hero's journey.
And the sphere grid is the best "leveling up" mechanic in the series by leaps and bounds. While there may be some way to break it, it's beautiful, and the fact that the whole part can use it at once I find to be extremely elegant.
Final Fantasy VI
Ok, I should disclose that this was the game that got it's hooks into me as a young teenager, several years before many people had the same thing happen with VII.
But I still think that the characters of VI are the best in the series, even though they're 16-bit sprites. The sprites might not be very expressive, but the characters make up for it with memorable stories in the text. It's also worth pointing out that VI is the only game in the series that features a villain that at least starts out human. Kefka may be crazy(the explanation of why is hidden as a minor anecdote, but still thematically appropriate), but that he is human and capable of, say, being imprisoned by his own emperor changes how we should regard him and his actions.
I also think that the art isn't bad: most of the backgrounds and monsters are very polished 2d sprites with a good degree of detail. Sure, the monsters might signal their attacks by flashing, but the abstract nature of the combat doesn't necessarily detract from the strategic element. If you don't think that you need a game to be 3d to be pretty, then I think it stands up pretty well.
Alright! I hope you enjoyed it!