Don't know if you talking about baseball or football here.Atlanta in January,I suspect,isn't *that* bad.Not as bad as Green Bay is,at least.But if my experience visiting Tampa in October is applicable here then Atlanta in June/July/August has got to be unbearable! Open air...Atlanta...July? No thanks!
Talking about the football stadium. The Braves stadium is very nice. It does get hot and humid here in the summer.