FF1 - Never played
FF2 - Never played
FF3 - 0/5. Boring, the ancient crap way of JRPGs. No characters, no story, just a string of dungeons and fights with inane cookie cutter story to somehow bridge it together.
FF4 - Only played the first 5 hours or so, can't judge it.
FF5 - I beat it but it's been 15 years so I'm not gonna rate it. I liked it back then.
FF6 - I beat it but it's been 15 years or so I'm not gonna rate it. I was absolutely blown away by it as a teenager. The large cast, the amount of secrets and side quests, the story twists, it was the best the genre had to offer at the time. I just can't say if I'd still enjoy it nowadays. If they make a remake that doesn't suck maybe I'll replay it sometime.
FF7 - 5/5. My first FF. I think most people always hold their first FF in the highest regard. I put 100 hours into it on my first playthrough, had all characters on Lv99, etc. I've never done that again for any other JRPG since. The amount of secrets and side quests was mind blowing, there was so much to explore and discover. The story was totally unique at the time. It had IMO the most rewarding character building system with materia. It was so much fun to create completely ridiculous and overpowered materia combinations. The cast seems emo and dumb in retrospective, but hey, I was a teenager back then and it was the shit at the time.
FF8 - 3/5. Coming from FF7 I didn't like it back then, but I replayed it in recent years and I softened up a lot to it. I think it actually has a much better cast than 7. The story is ruined by the horrible nonsensical "twist", but up to that point it was stupid (really, having schools to turn kids into soldiers?) but engaging at least. Edea was a pretty wicked villian (again, until the twist). Also Rinoa = best waifu in FF. Gameplay wise it was an experiment that failed IMO. The whole drawing spells thing was just tedious and that the enemies scaled with you was a bizarre design decision. With triple triad it had the best minigame in FF history though.
FF9 - 1/5. Terrible character design (Steiner is the Tingle of the FF franchise), meh story that also got ridiculous near the end, unengaging battle system.
FF10 - 5/5. Good cast, decent story, great character customization with the free sphere board, first FF where you could break the damage cap (it is amazing fun to smash an enemy with a 99999 attack). Good amount of secrets and endgame bonus content.
FF10-2 - 2/5. Interesting experiment, but didn't succeed. Too fragmented into episodes, too random in content jumping from fighting to strange minigames, WAY too much missable content, without a guide I find this game near unplayable. The story didn't make a lick of sense. 2 points for Rikku being a main character
FF11 - Never played.
FF12 - 4/5. Meh cast (I only like Basch and Ashe), cookie cutter story. But the realtime gambit battle system was IMO the best in the series. Also fun character customization with the job board thing, though it wasn't as interesting as the sphere board. Still, I love this one purely for the gameplay.
FF13 - 3.5/5. Underrated, people always cry about the linearity when they don't give a crap about that in 50 other games. The cast is great aside from Hope and Snow, the combat system is very good though the game does take its sweet time actually make you make use of it properly. Starting from when the world opens up it's pretty great throughout gameplay wise with lot's of cool battles. The story is decent, though I'm not sure I ever really understood it 100%. The world has a lot of strange rules that never really make sense and the sequels didn't help with that, they rather made it more convoluted.
FF13-2 - 4/5. Good story, good combat, though it sucked that the third party slot was reserved to monsters or OP DLC characters (seriously, having Lightning there breaks the game. And doesn't make any sense from a story perspective but who cares). Cool time travel area puzzles. Very underrated game (probably because people talked themselves into hating 13 so much they didn't give this one a chance).
FF13-LR - 3.5/5. Super experimental game. It's full of unique and interesting design decisions. The biggest one is probably that you don't level up or get strictly better equipment, instead new gear is about opening more options. It was definitely a breath of fresh air. Didn't beat it because the difficulty jumped like crazy near the end.
FF14 - 2/5. Good story I guess (I only played through the original without expansions) and great high-level content (dungeons, raids). But getting there is so painful I have a hard time recommending it. The quest design for the first 50 hours is completely inane garbage and some of the worst shit I've ever seen. The game thinks it's clever by claiming it knows that it's terrible quest design, but putting a wink on a quest to hand out soup to 100 soldiers right before a crucial battle, does not change that it's a quest about giving soup to 100 soliders.
FF15 - I just wrote about it in the Victoly thread, go look over there.
FFT - It's been too long so I won't rate it. But I hated it back in the day when I gave it a try. Japanese "strategy" RPGs are pretty much always terrible. It's not strategy when it's about having grinded the right jobs to a high enough point. I remember the difficulty being all over the place. Then I came to some important boss fight and it was pretty much completely impossible with how I had build my character according to guides I checked. Fuck that shit.