Horrible story & characters and a battle system you can break fairly easily.
Everything about 8 is horrible, including the combat system which can be exploited to make the game ridiculously easy. The main villain is horribly underdeveloped, literally no backstory or motivation whatsoever. It's just a bad game, don't bother with it.
5 is decent enough gameplay-wise, but there's no real story to it. It's pretty forgettable, don't bother with this one either.
1-3 are playable if you want something really old school. they are primitive compared to modern games. They are still kind of fun imo.
4 and 6 are better than 1-3(not sure about 5). 6 is honestly better than 4. 7 is influential, but the graphics make it feel dated, and the battle systems uniqueness no longer feels as unique. Its worth a play -through, but future entries are better. I can't judge 8. I've heard mostly negative things 9 is great. Personally my favorite, so I might be biased. I suggest this one, as long as you don't mind oddly animalistic characters, which is kind of weird. Still, the artstyle is really nice, the battle system works well. 10: Some good stuff in here. Voice acting is a bit annoying imo, but I am really picky so maybe not. The Gameplay is kind of oldschool, but in a good way. The level up system is alright, people seem to like it. Keep in mind the game is more linear than previous entries in where you can go (I think it opens up at the end, but I never beat it) 11 is an mmo I have never played. 12: I like the game play in this one. The story is different from the others, and the map is very open. Gameplay is differen from previous entries. 13: Skip it. Even more linear than 10. The battle system had potential imo, but failed to deliver. The story is convoluted. If your curious watch a lets play or review.
There are some good side games. I recomend the final fantasy Tactics series. The first one has a great story, and great gameplay. The two sequels are unrelated and have terrible stories. In addition they are pretty easy, while the original was one of the harder tactical rpgs out there. However, there is LOT more game play and are still really fun.
The other final fantasy game I'd recomend is one nobody talks about: Final Fantasy crystal chronicles. If you have friends and want to buy the supplies to play it(Gamecube and gameboys + link cables, you can get a fun hack and slash adventure,
Edit: Just realized right as I posted that this was the ps3 board. I'm keeping it up because It still might be helpful