FFIII
Old Opinion: This was pretty good, not great but still pretty fun.

New opinion: Playing the original version definitely jumped this entry up on my list. The job class and hands off story work better when the game is actually challenging.

FFIV
Old Opinion: It was good for it's time but boring now.

New Opinion: This game was way more thought out than the other entries. It still has problems but my researchanalysis has given it more respect in my book.

FFVI
Initial Opinion: Ugh, the concept is cool but RPGs have troutty combat and the menu system is impenetrable.

Old Opinion, after I stopped being dumb: GREATEST GAME EVER!!!

New Opinion: I still love this game, but I acknowledge it's myriad of flaws and how some people won't like it as much as me.

FFVII
Old Opinion: Kind of a let down. It started so good and then just imploded halfway through. Worse FF ever. I'm sure other fans will agree...

New Opinion: Okay, the fanbase is what made me really hate this game, but I acknowledge that it had some great ideas and simply suffers similar problems to my fave FF above. Course it's still way better than that piece of trout FFX...

FFVIII
Old Opinion: Definitely different and unbalanced, but still fun if weird. I would be lying if I said I didn't love this game a little more than I should because so many VII fanboys hate it for not being VII-2.

New Opinion: Flawed as hell, but I still appreciate what it was trying to do, and I still feel Squall's story is probably the only good writing Nojima has ever done for the series.

FFX
Old Opinion: It was okay. Honestly, I found it pretty boring overall and didn't feel any satisfaction by the end because of it. (Another playthrough later) Oh that's why, the game has no real challenge and the cast are annoying melodramatic fools all trapped in a really linear game experience where my only options are to go forward with the boring plot or play one of the games asinine mini-games...

New Opinion: It's got some nice ideas, but the execution of it all still leaves me cold. This game chose to be safe instead of innovative. Yet I take back my thoughts on the linear game design because at least it was something, not like that piece of trout FFXIII...

FFXI
Old Opinion: They made it into an MMO? How dare they!?

New Opinion: Whatever, that happened. Don't even remember why I cared actually. Oh hey look, XIV is an MMO as well.

There are a few where my opinions did slightly differ from initial playthrough vs. later introspection, but ultimately the change only shifted ever so slightly for the better or worse and my initial feelings largely stands; so I'm not going to bore you with those.