I haven't retired to PR, but I can chime in a little bit. I lived on St. Croix, one of the U.S. Virgin Islands, which is not far from PR. They sort of consider PR "the big city," and if you don't want to go as far as Miami, it's where you go for medical care, shopping, etc. that you can't get on St. Croix.
One thing I noticed while living there for a year was that, although I enjoyed the beaches, little restaurants, time with friends, etc., I felt a little bit trapped. Rock fever, they call it. You can't go more than about an hour from your home (obviously farther on PR, but same idea) without getting on a plane. There's only so much island to explore before you run out of island. On PR you do have the advantage of having a large airport (most flights to STX go through PR), but you're still looking at shelling out some money for a flight any time you want to go anywhere, even if it's just hopping over to the next island.
The comments about the culture sound very much like St. Croix. Island time really is a thing, and if you're not on vacation, it can get to you. As noted, sometimes it works in your favor. The cashier who is making you wait while having a long conversation with the person in front of you will also have a long and friendly conversation with you. If you're retired, that might be a nice way to live. If you're racing around to get things done on your day off like I always seemed to be when these things happened, then it's not quite as pleasant. Just something to keep in mind. On the other hand, if you want to have a little side hustle or post-retirement mini-job, people might very much appreciate your mainland standards of promptness, etc.
Before I moved to St. Croix, everyone recommended that I do a PMV (Pre-Move Visit) of at least a month, during which time you live in a place with a kitchen (assuming you don't plan to eat every meal out once you move there), drive some routes you would commonly take if you lived there (post office, bank, etc.), shop at the grocery store, etc. Sure, enjoy the beaches and stuff, but don't treat the entire month like a vacation. Treat it like a research project to see if you'll truly enjoy living there. I did it, and it helped. I probably would have continued to live there beyond that first year if my job hadn't been the worst job ever.