Not living in Chiang Saen, I've visited a few times.
It depends on what you think you need, AFAIK there is only one government hospital in Chiang Saen, nothing private. I doubt there would be much of a bar scene for expats either, or a range of restaurant cuisines. IMO you would need to be fluent in Thai.
I moved from Chiang Mai to Chiang Rai two and a half years ago. Chiang Rai is laid-back enough for me, with all the facilities I need.