I spent 95 hours over a few months, did all but one super late game boss. I also went back and played the early game again to see if I missed anything early on. There's a lot of optional content not necessary to the story but adds a bunch of depth. Kinda felt like final fantasy 10 and collecting the ultima weapons to take on end game bosses.

I think you can rush through the game in 15-30 hours and get most of the story. I'm not a completionist in any way but getting most of the dungeons and upgrades and beating some hidden bosses took me about 60 hours. I also didn't feel the run time at all; The fighting system can be a lot of fun and there is always an interesting dungeon mechanic or twist on an old boss around the corner.