I have played every mainline game, barring the MMOs (but you knew that). The only one I haven't finished is XIII.

Final Fantasy's very nature is change. Every entry is different from the last, and that's what I love about it. I've found some--often lots--of enjoyment in all of the games. However, it's a frequent feeling that one of the games are "perfect", but with some critical flaws. It's not uncommon for said flaws to be incredibly frustrating.

Case in point.

Final Fantasy I-III are a solid trio. I like II the most, because I'm weird, but it's obvious these games are the NES ones. I still like them a good bit, and believe they're worth playing. At least, the Pixel Remaster versions are. This is true for I-VI, but the SNES games hold their own better.

Final Fantasy IV is a great balance of gameplay and story quality. It's also challenging. However, it's just a little mid.

Final Fantasy V. Excellent gameplay. Fantastic music. Interesting world. Boring plot. Gilgamesh.

Final Fantasy VI. Great music. Outstanding story. Incredibly well designed world. The gameplay is fundamentally not good enough. Suffers from cavern syndrome.

The PSX games are generally great--specifically IX--but the dungeons backpeddled hard because of the single-screen nature.

X is too.. I don't know. I love X, but something is just missing here. I don't know how to put that into words. It's probably just that PS2 jank. The game feels a little weird. Else? Beautifully executed combat, incredible progression, good enough world that still suffers from PSX syndrome, and--oh, there it is. No overworld. It's dungeons and hallways, then what is practically a PNG with dots.

XII. Incredible in all respects, but the story beats just aren't quite there. Most of the games have a more engaging story loop. Possibly the most perfect game in the series, when the only real criticism is that the story isn't perfect, but everything else is.

XIII, no. Don't think I hate it, though.

XV feels half baked, but the potential for an incredible game is there. It's obviously there. Regardless, it's fun. I liked it. I wish it was better, but I'd rather the game exist in its current state than not exist at all.

XVI. Good lord, where do I even begin? Best lore in the entire series, easily. Best protagonist and antagonist, best cast at that, arguably the best music, fun combat, dogshit progression, world and side quests. Something is wrong when the NES game has a more engaging progression loop than your literal flagship PS5 title. This is a sore spot, as I absolutely love XVI.. but I can't stress enough how absolutely agonising it is having the entire combat system offer exactly one weapon, one style of combat the entire way through. Everything is based on the eikonic abilities, which is fun, but the time spent waiting for those to recharge is the same fucking SLASH, SLASH, SLASH, SLASH, pause, repeat, magic burst. It's infuriating. This is the least balanced game in terms of the quality of its foundation, it's seriously all over the place.

I love this series, despite its flaws. It's really hard to get me to play fourteen of something, so they clearly had an effective formula. My favourite is XII, naturally. Follow with V and IX.