I have been playing Final Fantasy Tactics for about a week. It was the first time I played it. And what an exceptional game it is! Yay!
It kicked off all the other "tactical role-playing games", and is still a class all by itself. And while there isn't much you can do to influence the plot, it has all the other things you would want in abundance: a superb levelling system (very fast, with lots of options to choose from, but very balanced at the same time, you start out weak and can "abuse" the game to become super-powerful), a very interesting story, a large replayability and a huge customization.
It's the game Diablo III and StarCraft II hope to equal, with better graphics. And it helps FFT doesn't run on a PC, while SD and Diablo I and II only do.
But, what does that have to do with an open-world sandbox like the Elder Scrolls games?
While the ES games offer (hopefully) interesting views and places, and you can decide to do what whenever you feel like it, that's about all that is left in Oblivion.
While there is a different market for set-piece battles (StarCraft, Diablo, Fallout (Tactics), chess, etc), most everything else has tried to do that in first-person perspective. And most of them (including all the FPS Final Fantasy games) failed miserably at it.
So, what I would like best, would be a cross between Final Fantasy Tactics and Morrowind.