Can someone give me a TL;DR version of which entries are worth playing? Apart from FF VIII, I also played Knights of Xentar, probably about the first 50%, and that sums up all my experience with jRPGs. Never played a console game in my life.
The original Final Fantasy for the Famicom/NES is not in the JRPG subgenre but rather a game derived from Wizardry, Ultima, and directly from Dungeons & Dragons, without much of a narrative and without characterization. It is worth playing for someone interested in the roots of the series and is pretty decent in its own right.
Final Fantasy IV (originally released outside Japan as Final Fantasy II) on the Super Famicom/NES is very much in the JRPG subgenre, with a lengthy narrative centering around the protagonist, along with various other characters who move into and out of the party, beyond the player's control, amidst a multitude of cutscenes, while combat and exploration are simplistic. It also introduced the "Active Time Battle" system that would continue in the next five games in the series. Worth playing.
Final Fantasy VI (originally released outside Japan as Final Fantasy III) expanded the length to about 40 hours, which would be standard for the next five games in the series, and otherwise continued in the JRPG tradition but now in a steampunk setting and with an ensemble cast. Also has the best music of any series entry and probably of any videogame ever made (series composer Nobuo Uematsu outdid himself here), despite the technical limitations of the Super Famicom/NES. Definitely worth playing.
Final Fantasy VII was a bit of a cultural phenomenon in its day, but the leap to the Sony Playstation and 3D graphics was awkward. Has a nukepunk setting, and starting with this game every entry in the series has many FMV cutscenes in addition to regular cutscenes. If you enjoyed Final Fantasy VIII, you'll probably enjoy this one, if the graphics don't bother you too much.
Final Fantasy VIII tremendously improved the graphical quality over its immediate predecessor, despite being released just two years later and still on the Sony Playstation. Has an irritating cast of teenagers, level scaling, and a semi-futuristic setting that doesn't really cohere. Wouldn't recommend except that you stated you enjoyed it previously.
Final Fantasy IX harked back to the Famicom/NES and Super Famicom/NES games in many ways, while adopting a cartoonish aesthetic relative to the realistic graphics of its immediate predecessor. Has better themes, plot, characters, and gameplay than the other two Playstation Final Fantasies, with a vaguely Baroque 17th-century setting. Worth playing.
Final Fantasy X made the jump to being fully 3D on the Playstation 2, with a post-post-apocalyptic setting and voice-acting (not full voice-acting, but fully in cutscenes). Combat reverted to turn-based, while greater linearity meant exploration was reduced from its already-limited amount. This is the last Final Fantasy with new music by Nobuo, but he only contributed a portion of the soundtrack, so the overall quality is much lower. Looks gorgeous, but I wouldn't recommend except that you enjoyed Final Fantasy VIII.
Final Fantasy XI is an MMORPG, as is its successor Final Fantasy XIV; these two shouldn't have been numbered entries in the series.
Final Fantasy XII is 50% longer than it should be, while having horrific MMORPG-influenced combat in which the player mostly just sits and watches the characters act according to a simple set of if-then statements that the player has inputted. Avoid.
Final Fantasy XIII on the Playstation 3 butchered combat in a different way from its immediate predecessor, while also nixing exploration in favor of running down an endless tunnel/corridor (there aren't even any cities/towns/settlements). The tutorials last over half the game; it isn't until after the midpoint that the combat options are fully unlocked. Also, the characters are the worst of any game in the series. The worst RPG I've ever finished.
Final Fantasy XV was stuck in development hell for a number of years before releasing on the Playstation 4, and the result is an awkward mix of Open World with a sort of Action RPG combat probably influenced by Dragon's Dogma. Notable also for having bizarre tonal dissonance, established quite early in the game, between a road trip for the four party members (all established friends) and a grim tale about the destruction of the protagonist's kingdom and possibly the entire world. Nothing about the game is much good, though it's still better than XII or XIII. Avoid.
There's also II, III, V, XVI, and the many, many offshoots, sequels, or otherwise random games with the Final Fantasy name attached.