Costs:
Depending on what costs you are looking for, some are high and some are reasonable. If you want to buy a condo in Panama, now is a pretty good time. There is a huge influx of condos hitting the market now and the inventory is immense. This means most are priced competitively and you have lots of selection. Food, clothing and other day to day costs are getting to be comparable with North America, if not higher. In the last three months of 2011 food prices increased 30%. It's one thing to pay the prices but it's another to realize the quality is lacking for what you are paying for.
Climate:
Like everywhere else in the world, the climate is changing in Panama. Every year the wet season seems to start earlier, therefore shortening the beloved dry season. This past may feels more like September/October with rain almost every day. Three years ago there was practically no rain until June. This year it started in April! Despite the rain, Panama is hot and steamy year round (85-90+ every day), although the dry season brings a refreshing breeze. I can't tell you how many people move here without spending a good amount here first, then have to move elsewhere because of the humidity. Live here a year with all the seasons and then decide whether you can cope with the weather.
Medical care:
Excellent - The doctors speak English and most have been trained in either North America or Europe. What you have to pay for a doctor or dentist is a fraction of what you would pay in the U.S. That all being said, make sure you have a good medical insurance plan,
Lifestyle:
You can make it what you want it to be. You can live as fast as you want or as slow as you want. If you a partier, there are lots of clubs and bars that would surely fit the bill. If solitude is what you are looking for, perhaps living in the city isn't for you - lots of noise, construction and traffic is excrutiating. There are lots of expats here and some are open to receive new friends, some not so much. You have to look around. Panamanians are very tight-knit and more often than not you will not have serious friendships with them. The biggest complaint among expats is the lack of customer service. Depending on what kind of person you are, this can totally ruin your day or merely upset you for a few hours then you move on. Regardless, you WILL be affected.
Best thing to do is come down for a year and rent a place. There are lots of furnished rentals. After one year you will have a pretty good idea what you are in for and then you can make a somewhat educated decision at that point. Panama is not the cheap haven it once was and because of that, many expats are leaving to make their fixed incomes work for them, even back in the U.S.