I STRONGLY suggest Kingdom Hearts I and II. If you've read my review on the forum, it gets pretty in-depth on the entire game. I may 'only' give it a B+, but I haven't given any more than a B to any other game in my history of playing, so.
I also strongly, but not as strongly as the KHs, suggest Xenosaga Episodes I and II. Super complex story stuff, fun, entertaining battles, a lot of sidequest stuff to do, etc. and so forth.
I'll have to politley disagree on the Nippon Ichi games. They're kind of dumb and, while their battle systems are complex, the battles themselves get boring. Not to mention you don't ever feel like you've actually accomplished anything by beating them. That's just one man's opinion, though. So.