Yah, Nippon Ichi games are the way to go if you like tqactical RPGs at all. I personally am addicted to Nippon Ichi games. The very first video game I ever played was a Nippon Ichi game, I can't recomend them enough. But, on the other hand, I love Xenosaga.
As for other RPGs, I would say that if you haven't gone for all of the old school Final Fantasys, that's woth a shot. (Anthology, Origins, ect) As for openness, (please no one shoot me) but after playing FFX, you might like FFX-2, because it is super open. Pretty much 80% of the game is side-quests that have their own seperate plot. You can rush through the game to the end in only a few hours, but then you will have no idea why anything happened, you actually have to go out of your way to discover the whole plot. I like that, but most people thought that FFX-2 was way too lame. I will admit that the "Girl power! Lolz" got old quite quickly, but how can you not love a game with henshin sequences?