FFIX's setting, narrative and characters, blended with Final Fantasy Tactics' larger cast and job system/customizability. Really, I liked the combat found in FFIX.
A linear campaign is alright so long as it's split into many parts, allowing exploration with plenty of optionals and Easter eggs in between. Stick to the older looks for the characters rather than this gloomy, spikey haired silliness we've had off and on for two decades now.
I also wouldn't mind just chuckling voice acting out the window as it's generally terrible. Even more modern installments like VII-IX did just fine without it. Less cut scenes or, at the very least, allowing the player to skip them would be great.... Don't need to watch Tidus and Yuna engaging in some awkward PG romantic swim-dancing with terrible japanese pop music playing in the background for ten minutes... It felt that long at least, don't really know how long it took.
That reminds me, the music. Again I think IX had the most great pieces of music, but others had great music as well. Tactics, X, VIII, VI... Really, the music is always great.
As for villains, it's hard to beat Kefka or Sephiroth. I thought Sin was actually a cool new enemy as something that lacked personality and dialogue, but rather was simply a tragic, inevitable, impending doom; it was a bit like the Borg. Something different and clever like that might be nice.
If a game met just a few of those I'd live it.
