Phantasy Star III is probably my least favorite of the original series, but I hardly hate it. My relationship with the game goes back to the early 1990s, when I was anticipating more of a direct follow-up to Phantasy Star II. III was a major disappointment in that area, combined with the fact that I prefer sci-fi over medieval RPGs. To make matters worse, what was supposed to innovative about the game (the multiple generations) turned out to be more of an excuse to recycle dungeons and worlds within the game. Bah. The stories are riddled with inconsistencies and irritating plot loops. I would argue that you walk around more in PSIII than PSII because of all the darned backtracking.
I was so sick of seeing Divisia's dungeon and the western cave in Aridia by the time I had gone through all the generations I could have screamed. The battle system was also a disaster. I ended up not really liking the Choose-Your-Wife generation system because there were absolutely NO female leads. What the heck, Sega??
The best part of the game, and what makes all of my above gripes worth it anyway, is that the characters are really well-done. We're also introduced to andriods/cyborgs as playable characters (and there's my love of sci-fi coming through). I also find the game more enjoyable if I think of it separately from the rest of the series. It's really an innovative idea (being lost in space and not knowing it) that was poorly executed. Perhaps it was too far ahead of its time and Genesis was not the right platform. It could use a remake.