Okay. I'll write a brief review on 1-12, and exclude all the FF games that weren't part of the series (like FF Tactics, my favourite, FF Legend, FF Adventure, FF Crystal Chronicles, Crisis Core FF7, etc). Otherwise, I'd never finish!
-Final Fantasy (1): For its time, the graphics weren't a problem. It's nice that you could pick your job. The battles and dungeons in the original were actually challenging (unlike in today's games), however, characters lacked personality and the story had some fun elements for that time, but was still weak. GBA version's graphics were pretty, and the game was somehow easier.
-Final Fantasy 2: I liked it, many people hated it. Maybe it has to do with the fact that i didn't get very far into the game until I played Dawn of Souls, the pimped GBA version. The battle system was tricky but not bad. Characters did have a personality in this one (my faves are Minwu and Hilda), and the story was more solid than FF1's. Also, the new dialogue in the GBA version was beautiful. A lovely game.
-Final Fantasy 3 (the original, NOT the DS remake... haven't played DS remake yet): Like 1 & 2, graphics weren't its best feature, although they were fine for their time. The story and characters, however, seemed to be heading backwards, as they were more like FF1's and less developed than FF2's.
It did have some nice bits though - the stories of characters like Elia, Desch and Allus were somewhat interesting.
-Final Fantasy 4: One of the best in the series. The graphics were awesome for SNES. Amazing characters, interesting story, and good dungeons. It had a mature, admirable protagonist... which i think is uncommon in RPGs.
Like all the old FF games, the battles were quite difficult! Although I like a balance, I think difficult is at least better than too easy.
-Final Fantasy 5: The diverse job system was fun! I played each version, but preferred the Advance port mainly because of the witty new translation.
The main characters had a great deal of potential, but sadly didn't receive much development. Other characters like Gilgamesh were simply awesome.. hehe.
-Final Fantasy 6: Another gem, a landmark for the series, a masterpiece! It had an excellent cast of deep, interesting and well-designed characters, a very good, complex story that didn't feature a princess awaiting rescue, some of the most impressive FF scenes (like the opera scenario, for example), and one of the spiffiest villains ever!
The battle system was far superior to those of FF1-5. The graphics, monster design and landscapes were wonderful for SNES. So was the music which I still find myself listening to almost every day!
-Final Fantasy 7: Another masterpiece. For its era, the funky graphics were actually legendary. The music wasn't any less beautiful than FF6's. Great characters design, great dialogue, great battle system (although easy for the most part), great mini-games and side-quests, great.... atmosphere (there was something about the atmosphere of areas like Midgar, Nibelheim and Junon that I couldn't quite describe). The characters and storyline are unforgettable.
-Final Fantasy 8: The worst one in the series (that's NOT counting FFX-2 which to me isn't part of the series). FMVs were pretty, I'll give it that; as for the overall game graphics, I preferred the older ones... even 7's.
The story was kind of poor and the majority of characters weren't much better. Well, Laguna's portion was nice, but unfortunately it wasn't the focal point. There was hardly anything that made me beat it other than wanting to beat all the FF games I owned.
What made it worse is that when I had finished FF7, I was eagerly awaiting the next installment, so i followed the commercials, magazine articles and all the hype about FF8 which gave a good impression. But I was sorely disappointed..
FF8's strongest aspect is, without doubt, the music. Fantastic OST, I can't deny that!
-Final Fantasy 9: Another not-so-great FF, but still better than 8. It's simply mediocre. The characters weren't bad, but the story was kind of weak for a FF, in my opinion. FMVs were awesome, but the gameplay wasn't. Again, it did have a strong point that is its music. Not half as fantastic as FF8's OST, but it did have some great pieces such as Melodies of Life!
-Final Fantasy 10: A beautiful game in terms of almost everything - character development, plot, design, graphics, music and fun. Some of the main characters were annoying (eg. Tidus, Rikku, Yuna), alright, but they did each have an intriguing background.
A lot of people didn't like the game itself but enjoyed the gameplay and battle system. I'm quite the opposite - I LOVED the game but wasn't very fond of the sphere grid and the battle system. FFX had one of my favourite game endings. Too bad FFX-2 came and ruined it. I'm not even going to go into FFX-2... It was horrible.
-Final Fantasy 11: i would have much preferred it if they didn't release as part of the series (the 11th), but instead as 'Final Fantasy Online' or something. I didn't play it long enough to reach a conclusion, but what I've experienced of it was enjoyable indeed. It's probably the best online game I played, but that was back when it came out. I don't know how much it's changed since.
-Final Fantasy 12: A good game, albeit lacking in character development. I loved the characters, but I thought they weren't given enough attention by the creators. The missions were ok, but not really my area of interest. Battle style reminded me of MMORPGs, and I really enjoyed it as I've always been a fan of applying strategy. I like the license board, and the espers! and of course, the slight resemblance to stuff in the original FFT.
I noticed that the odd numbered old-school FF games (FF1, 3 and 5) focused on gameplay aspects, while the the even numbers (FF2, 4 and 6) focused more on storyline and characters.
Well, that wasn't very short after all, but I did try not to go into too much detail. XD