In this one I'll cover Final Fantasy X and Final Fantasy XI. I'm not touching X-2 (Haven't played), XII and XIII (Too recent for a "retrospective").
Final Fantasy X (2001)
Final Fantasy X marked the series transition to the next generation of consoles. The game took advantage of the PS2's vastly superior hardware to produce full 3D effects (as opposed to the ones seen in the previous games) and incorporated near-full voice acting. Due to the player being able to name the main character, some scenes weren't voiced due to this.
Just gonna get this out of the way riiiiiight now.
Corny moments aside, this game made a few interesting strides in terms of gameplay. The Sphere Grid system replaced traditional leveling. As you gained enough experience points, you gained "Sphere Levels", which allowed you to move along a grid. You could activate the space you were on, and spaces adjacent to you if you had the appropriate spheres in your inventory. Now, at the start, each character was on their own path, so they were distinctive (Auron had a lot of HP and Attack spaces, Tidus had Speed and Evasion spaces), but if you used the right special spheres, you could jump into someone else's grid, or learn an ability they learned. It was a different approach to leveling up your character and was kinda fun in my opinion.
The next gaming convention was a slight modification of the Active Time Battle (ATB). In past Final Fantasy games, your turn order was determined by a filling bar on the side that filled faster if you had higher speed. In this game, the bar is gone, but you have the same concept. The turn order is displayed on the side, but certain moves (Tidus' Quick-Hit for example) would make your character's next turn come sooner. Other moves had a chance to delay an opponents turn as well. In addition to all this, you could switch out your party members mid-battle if one gets hurt, or you need to switch from melee to magic.
The game also allowed you to customize equipment. Unlike previous games, two weapons of the same name could boast different stats. If you have a sword for Tidus, for example, it could have 3 slots. They can either be pre-determined with some abilities, or empty, waiting for you to fill them in. If you have the right materials, you could make a weapon that does more damage (Strength +5%) or poisons your enemies (Poisontouch). This, paired with the ability to change gear mid-fight meant that you could switch to a specific piece of armor to fight off an incoming elemental attack, back to your other piece of defensive gear.
Also in this game, summons (called Aeons) are only callable by Yuna, the female protagonist of the game. The nice thing about them is that they're controllable, unlike previous "Summon for big attack, then leave" summons of previous games. The Aeons can have their stats improved and abilities can be learned the same way you customize gear as well. This means Ifrit, a fire element Aeon can learn Blizzaga, a strong Ice Spell, which would make him very useful against fire-type enemies since he would receive minimal damage, but do massive amounts in return. Aeons also have their own Limit Breaks, which allows them to deal massive damage to all enemies.
"This is my Ass-Kicking pose"
The story can be a mess at times, and the main minigame, Blitzball (or as one of my friends affectionately calls it "Drown Ball") can be hit-or miss for people. Overall though, it's a solid entry into the series and is pretty fun to play.
Final Fantasy XI (2002 PC/PS2, 2006 Xbox 360)
Final Fantasy XI was Square Enix's first MMORPG, and predates World of Warcraft by 2 years. Now, what this game does is... well, a lot. It offers 5 playable races: Humes (general all-around stats), Elvaan (Tall elf-like, good Warriors), Tarutaru (Smallest race, cute, strong with magic), Galka (Strong bear like people, good Strength), and Mithra (All female race of agile cat-people... This is Japan after all.). There are also 20 different Jobs (classes in other MMOs) that you can play as, but only 6 are available at the start. Unlike other MMOs, you can switch your Job at your "Mog House", which acts like a safe haven of sorts.
Until you hit level 30, you can only be a Warrior, Monk, Thief, Black Mage, White Mage, or Red Mage. Upon reaching that milestone, you can undertake quests to unlock the other 14 jobs, which include series staples like Ninja, Samurai, and Dragoon. Not all the quests are easy though. Some you can undertake at 30 by yourself, others, you may need a party of 6 at level 50 to unlock a job.
In addition to being able to change your job to fit your mood, you can also synergize your Job by having a sub-job. Upon reaching level 16, you can do a quest to unlock the sub-job ability. This allows you to equip a second job. You would get all the benefits of the second job up to the level cap of 1/2 of your main job. For example, if you have a level 10 Warrior and a Level 10 Monk, going Warrior/Monk means that you'd be a level 10 Warrior, and a level 5 Monk. But if you also had a level 2 Thief, and went Warrior/Thief, you'd be a level 10 Warrior, and level 2 Thief still. The subjob doesn't bump up levels.
This system plays out nicely overall. If you want to kill for items (farming), you could go Thief as a main (for the Treasure Hunter ability, which helps drop rates), and sub Warrior for extra attack and defense. This sort of hybrid gameplay made the game feel fun. When I played the game solo, I'd want to unlock other jobs just to try other combinations. Of course, as in any MMO, there's a generally perceived "Right" way of doing your class-subclass combo, but still, it's fun to experiment.
There are three starting areas, which are major cities in the world. in addition to doing missions for them to progress the story, you can switch your citizenship for a fee. You need to make it to the city and go to their embassy, and request a change of country, and BAM, now you can do their story missions. There's a LOT of content in this game, and a lot of endgame stuff I've never even played.
This is not a very PVP-centric game. There's passive PVP in "conquest", which basically amounts to "kill monsters in this zone with your country's sigil buff active, and help them take over". If the monsters kill a lot of Players, the Beastmen take control of the zone, which means that there's no real PC help in that region. If your country controls the area, you can buy some simple items from the outpost, and deliver Outpost supplies, which allows you to warp from the region to your home country, and vice versa.
STAY AWHILE AND LISTEN
The soundtrack is pretty good, not just by MMO standards, but by game standards. Series veteran Nobou Uematsu had a hand in helping with the soundtrack, which showed in the quality of the music.
This game is still going today, albeit with a smaller fan base. The strong PvE endgame are good reasons for this though. The community is pretty open and friendly. The graphics are a little dated, and the combat may feel slow at times as well. The game is still receiving new content over 10 years after release, which is astounding. Once this game goes free-to-play though (if it does), you can be certain I'll be diving back in for another go.