Final Fantasy VII
Pros: With so many different kinds of materia, there are hundreds of different kinds of combinations that one can use to find the perfect attack/spell/heal. There are even materias that support, defend, offend, and add commands to your options. With materia, anyone and everyone can use any materia that you can find. So no one person has to be a "healer" or "attacker" or "magic carrier". Although different characters have more powerful attacks than others, and some characters limit breaks are supportive, or curative, any character can carry any type and as many materia as their weapons and armor will allow.
Cons: Materia takes a while to level up. Most times you spend a lot of time just fighting enemies just to level up your materia. And without fighting the Ruby or Emerald Weapon, it takes a lot of patience to level every materia in order to get the Master Materias. But even if you decide to fight the Ruby and Emerald Weapons, to get most of the powerful materias that will make the battle that much easier, you will need to raise a Gold Chocobo. This too takes time and money and a lot of patience. Also your items become very clustered, each time that you get a new weapon or armor. Although most of the weapons that you get, can be sold, as once you get a new one there is no need to keep the old one, there are some that should be kept, as they will be useful in the future. But in the end it pays off, with a little patience.
Final Fantasy VIII
Pros: Instead of using materia, as in Final Fantasy VII, in Final Fantasy VIII, one draws magic spells from their enemies, and use them to junction to certain attributes that your character has based on the Guardian Force that they are using. Guardian Forces are the "summon monsters" from Final Fantasy VII. But instead of summoning them from a materia, a GF joins with a character and with them they bring abilities that a character can use by junctioning spells drawn from other creatures to gain these abilities. The GF, use AP to level up so that they can lean more abilities for the character that they are with. If a certain character stays with a GF for long enough, when summoned the time that it takes them to respond to the character becomes faster, because they begin to "like" them. Also the weapon setup is much different than in Final Fantasy VII. In Final Fantasy VIII, you can upgrade your same weapon, instead of getting a whole new weapon, which alleviates the amount of items that you must carry around with you.
Cons: Drawing all the spell you need, from either a enemy or draw point, can get tedious. I don't think that it takes as much time as materia, but I guess that depends on the amount of spell that a player seeks out for themselves. Also, junctioning at first can be somewhat confusing, if you are just coming from playing Final Fantasy VII. Also, latter in the game, when needing all the characters in your party to have specific abilities, sometimes you must swap GF, and they are not as use to this character. Such as when battling Ultima Weapon and wanting all your characters to have "Auto-Potion".
Final Fantasy IX
Pros: I like that for the first time since Final Fantasy I & 2 on SNES, a player can have four characters in their party. Also each character in the game has a specific task, or ability. In this way, each character is needed throughout the game, and all characters seem to level up equally as they are all needed equally. Also the learning ability is based on the "stones" that one can collect, through battle. Each character already has all their abilities, they just have to collect enough stones to use them.
Cons: On the flip side, having characters that have said abilities, when one character is taken out of the game, or is not available, it makes it difficult to make up for that character in battle. Although this could be said to be a challenge, sometimes it is an annoyance. Also it seemed as though the character leveling up himself didn't seem to make much difference. As long as one got all the stones they needed, then they were at their peek.
That is just my humble opinions on why I like and dislike certain parts of Final Fantasy VII, VIII, IX. I cannot form an opinion on Final Fantasy X, X-2, XI, as I still have yet to purchase a Playstation 2. But fear not, I will someday and get a chance to play, what I am sure, are some great games as well.