I found that up until 13, most Final Fantasy's had that FF thing going on in many ways, whether I enjoyed the game or not. Sometimes there was more story, sometimes less, but usually had some similar battle system (even 12 as different as it was, had it), some kind of summoning, creatures like moogles or chocobos, and the like. Generally the stories were pretty good, but how they were executed might not have always been great. My first was 3/6. And at that time in video game history, it was REMARKABLE. Heck, the bad guy actually succeeds and destroys the world, becoming god-like, and you have to reassemble your members who've scattered to the winds and take him down. There was a good number of great side quests and hidden bits. So for me, that game hold a special place in my heart, haha.
I'll do the usual and number out the games and my thoughts on them!
FF1 - I played the remake of this one first. I never owned an NES so I hadn't played it until I got the PS1 version. It was fun. A good simple little RPG that was mainly dungeon crawling and grinding. But it was enjoyable.
FF2 - Dang, I never got far in this one. I played this just after FF1 on the PS1 remake. I found I had to battle a lot to make my characters into my desired 'classes'. It was a really cool system and I was impressed that it was able to be implemented on the NES when it was released. Sounded like it had more of a story going for it than FF1, but I never got far enough to find out.
FF3 - Ah, the class/job system was super cool. Again, played a remake. I THINK I beat the game, but I don't remember, haha.
FF4 - I owned this one and played it many many times because I only had a handful of games for SNES back in the day. Well, of RPG's anyway. The boss battle music is probably still one of my favourite battle tunes from the series. Great story, even though limited with the 2-dimensional story-telling that lots of older games had. But awesome stuff with the whole dark knight/paladin thing, the lost brother being your prime enemy, the EFFING MOON. Pretty rad stuff. Zeromus coming outta nowhere was a bit weird but hey, he made for a gnarly final boss, haha.
FF5 - Played this one on the PS1 release as well. It had some of the same 2-dimensional story-telling as FF4, but you could tell it was more fleshed out. A bridge between 4 and 6. The job system was pretty killer in this one, with levels in multiple jobs giving you access to another, being able to equip job skills, and all that. I don't remember much of it though. The story was pretty forgettable, I guess, haha.
FF6 - My favourite, likely because of nostalgia reasons. I said mostly what I love about it in my opening paragraph, so it's pretty much all there. Edgar FTW!
FF7 - I got this game after finding out that Aeris bites the dust, so when that happened in-game, I didn't get it in the feels

Thanks, friends from grade 7. BUT it was a pretty cool game, even though I couldn't stand the Cloud's weird emo whine and didn't think Sephiroth was a good bad guy, motivation-wise. Your mom being an alien and you being created doesn't seem like enough to tip you off your rocker. I felt like he went crazy too easily. Maybe that was lost in the English translation, and I'm sure it was the translation that got me confused a lot when I first played the game, haha. But it was a good one nonetheless!
FF8 - The first time I played the game I must not have leveled up much and when I got to Pandora or whatever, I couldn't beat the witch boss there who was holding Rinoa captive, and all enemies gave me 1 exp, so I couldn't leave the place and I couldn't grind. Had to get a friend to load up a save file on my memory card so I could resume the game, haha. It also had some weirdly confusing and convoluted bits. I hardly remember the story being coherent. At one moment this was the story and then all of the sudden the story was something else. The GF system was cool, though. I liked that. And it made Alexander my favourite summon of the series, haha.
FF Tactics - Amazing game. Super sad ending. A bit of a letdown ending, actually. But the game itself all the way through to then was great. A+ with the job system and combat balancing compared to other tactical RPG's I've played.
FF9 - Overall I loved 9. Brahne and Kuja were kinda weak antagonists, with Kuja having sort of a Sephiroth thing going on. I LOVED how all NPCs were a blend of humans, anthropomorphic creatures and weird looking things. Such a cool world. Didn't care for how the late game phase closed off a bunch of towns and villages. That probably had something to do with disc space though, I'm thinking. I also enjoyed character-tied classes coming back. The story, the look, the feel, the skill learning system, were all things I vibed with in FF9. Probably my second favourite of the series.
FF10 - This was an odd duck. The sphere-grid was lame in end-game since everyone could learn all skills and I don't like that. Makes having particular characters a bit useless, especially if their design is based around their innate skillz, like Lulu being a black mage but then can be a tank like Auron? Nah, not a fan. The characters weren't all that interesting. Yuna was boring, Tidus was generic, Wakka was annoying, Lulu was a bit bland, Kimari was ok since his deal was stoicism, and Riku was a typical quirky character. Seymour's visual design was super lame I found, and an uninteresting enemy. Jecht's boss battle theme was cheese up the butt. And the lack of variety of aeons was disappointing. The story as a whole was pretty good but just fell flat on the delivery for me. It's an ok entry in the series, but definitely not a fav.
FF11 - Online and MMO so meh!
FF12 - At first I was like nah this is tedious, with the giant maps and looting for things to sell for money. Exploring the maps and getting sell-able loot took so long that I'd forget about what was going on story-wise. But the summons were a cool diversion from the usual FF summons and they all had some pretty great design and backstories. Got all of them. I really liked the battle system. Would be a great battle system concept for a Chrono Trigger remake. But same with 10, the ability to have everyone learn every skill was dumb. When I got to end game, I started doing the hunts and got lots done. About 100 hours in by little brother accidentally saved over my game file, haha. SO a couple years later I played it again, and knowing what to expect, I LOVED it. I even bought the remaster that came out last year or whatever, which was even better since the license boards were job-oriented and your characters could only have 2. Hooray, haha.
FF13 - A similar experience to 12 in that I played it, disappointed with how linear it was and the lack of towns/npcs/actual interaction with the world it had, got to Pulse, and stopped. I think I even sold the copy I had. But then a year or so later, I was like 'I should finish it' and picked up a cheap copy somewhere and enjoyed the rest of the game since I knew what to expect! Though the battle system was meh. I'm not a big fan of automated character actions. The thing Square-Enix has with having to have a unique battle system each game lately is something that doesn't interest me. But anyways, the story was interesting and big and I was a big fan of the mechanical design of the Fal'Cie, lol.
FF14 - Like 11 for me! Lame races! They all just look human with cat ears or just big trolls. BORING.
FF15 - Ah, the game that never was. No magic, lame summoning, hardly a story, you controlled only one character. Sure, it was a pretty game, some plot points were delivered with style and drama, and yeah the relationship between the party members was very well done, but that's it for me. A very short game with MMORPG-style fetch quests for sidequests? Guh. I traded in the game as soon as I finished. And I preordered the thing for 80 bucks. It's potential was there, but I think it was in development hell for too long and suffered because of it.
Let's just say my disenchantment with the FF series began years ago and now I don't think I'll ever pre-order one again, but I'll play them when they're cheap/on sale!