I may be the only peasant (read: no Hyatt status whatsoever except as a member) and I'm pleased to note that my stay was still great! On evening 3 of 3 at the moment.

Great:

• OMG the lounge breakfast buffet! Variety didn't quite match the Conrad buffet breakfast, but... sashimi and damn fine sashimi at that + a flavorful eggs benedict makes it a tie for me overall. Only nitpicks: no self-service decaf anything, and the decaf latte that was made for me was... pretty bad. And no matcha tea .
• Many things about my room! Big desk, reliable wifi, effective blackout shades, comfy bed (and twin size was, to my surprise, quite adequate for me as a single person), stellar shower, big bathtub, and nice city view from my 6th floor (I had originally thought, oh great, lowest floor, thanks a lot, so I was pleasantly surprised!). And not only a Nespresso machine, but their most powerful originaline capsule of the gods: Kazaar! Ah, and HVAC seems to work well!
• Evening lounge buffet was also great, with better hot foods that I've enjoyed at other lounges in Japan and just a lot of tastiness and variety overall.

Not so great:

• Location is mid. Not terrible, but not great IMHO. Nearest convenience stores are located in an adult-oriented area which I find mildly ugh and families might be a bit more concerned about ("Mommy, why are all these girls holding up signs with prices?"). More substantively, it seemed I had to transfer subway lines for nearly anything I wanted to visit in Fukuoka. Or walk 15 minutes to Hakata Station directly, which I guess isn't the worst thing in the world (especially during this decent Autumn weather).
• The bathroom has zero ventilation. Even a short hot shower fogs up the entire bathroom gobsmackingly bad so that even the underside of the glass sink gets all condensated up. Leaving the bathroom door open helps somewhat.
• Many of the staff quite struggle with English. I get it. I'm in Japan. I wish I could speak more than a few polite phrases, and it should be my responsibility to learn. At the same time, I do expect staff at high-end places like this to be a bit more proficient.
• As others have mentioned, wifi in the lounge is pretty bad overall (unusable 2/3 times I visited).
• Huge desk in my room, but a big lunk of a non-adjustable chair is kinda a bummer

All in all, would I pay 15-21K Hyatt points to stay here again? At 15K, almost certainly; that's quite a bargain for a hotel of this class, even with its faults. 21K (which includes an extra 6K for lounge access)? Probably not. I'd likely prefer to explore dinners out a bit, and I've learned I can buy the breakfast buffet for I think for 4450 JPY (~$29); given that I value 6K Hyatt points at a minimum of $120, that seems like the better deal by far .