I retired to Thailand in February (2017). It's winter here now and the climate in Bangkok is actually pretty nice. All summer the areas outside of Bangkok got a lot of rain and there was quite of bit of flooding. Yes. It is hot and humid for much of the year but I would say that the climate is similar to Florida, Georgia, Mississippi. I kinda like it after the cold and damp San Francisco winters.
I don't find the air pollution in Bangkok to be any different than Manhattan.
It can be cheaper to live here but, like everywhere else, location, location, location. I'm near central Bangkok on the BTS rail line and my condo is 55 sq meters for about $750/month. However, I moved from the San Francisco Bay area which is one of the most expensive place in the US to live.