Did you try Dragon Quest 8 on the PS2? It is as hardcore J-RPG as you can get, but it does it so well that you just have to love it, especially because there is so much to do and find. Great and especially long storyline also.
Even if DQ VIII isn't particularly easy, try to get your hands on Atlus games like the Megami Tensei (Nocturne, Digital Devil Saga or even the older NES/SNES games etc.) The content is more mature than all Final Fantasy and co. (and can even be really offensive like in DDS where characters must resort to cannibalism in order to fuel their demonic states and survive) and the difficulty level is nefarious.
(edit: there's a (long) retrospective article about the series here