I first played it around 2005, I think, along with Phantasy Star II and IV. It was the second PS game I finished. I think I finished it around 2009.
It's definitely one of my all-time favorites, and it's my favorite of the "big three," though PSII's atmosphere and music really get to me. Haven't been able to finish IV yet and for some reason I don't like it as much, but I can tell it's great. Just haven't gotten around to it.
That said, PSI's world is just unparalleled. I've never experienced anything quite like it.