10+ years working in Panama City. As SJOGuy says, it is NOT like the promotional media say: "just like living in the US! for $400/month!" In fact, I find only local staples cheaper (at best), everything else is more expensive, except for labor. It's very hot and very humid every day of the year in the city and most of the country. The city is chaotic every work day. Anything you want to do is generally a bit more dysfunctional, or aggravating. The dollar is good. Flights to here are good. The main highway crossing the country is now very nice. Internet is pretty good. Cell service is poor. I have little or no safety concerns, although my windows all have bars. Water system is iffy. Electricity goes out once a month or more for no apparent reason. I am very pleased with medical care.
That being said, I would have no qualms retiring to Volcan, with its clean, crisp air up in the mountains. Boquete is similar, just more expats and more developed. El Valle de Anton is not as cool, but it's closer to beaches, and the city. Lotsa expats retire to the pacific coast west of the City. The beaches aren't that good, and the weather is still too hot for me, but I understand the appeal. Some decent golf courses throughout the country as well.