FFIX is the last game that was "magical" for me - in the sense that it completely transported me to another world when I played it.
I've played dozens of game since IX that engrossed me, but FFIX had such an amazing world and cast of characters and came out at just the right time (I was just turning 14) that it really was the last game to ever give me the same feeling that FF6, FF7, Chrono Trigger, Earthbound, etc, did in the past.
I'm so glad I got to experience those games as a child. And it's fitting that FFIX was the last one I played with a young, impressionable mind. By the time X came out, I was in high school and teenage angst had kicked in. My childhood was all but over, and games since then just haven't had the same power over me.