Just because their likelihood of winning aren't good, that doesn't mean they are overrated. For example, Heather Wilson of NM was a VERY STRONG candidate for Senate in 2012, but she ran in a presidential year and was still very competitive.
I think you need to better define "overrated" here. Tom Kean Jr. for example was "overrated" when he ran for the GOP. He should have been much, much more competitive and Menendez never even sweated during that race.
For the candidates offered up, it's a little difficult to separate the two.
Polling currently indicates a close race in Georgia, probably because Michelle Nunn is a stronger candidate than whatever a Generic Democrat is in Georgia. The question I believe you're asking is--as a candidate, is she so strong that she transcends Georgia's partisan lean, and will win in November?
That's a little difficult to separate from "Whose chances are overrated/underrated?"
Heather Wilson ran into the same problem as Robin Carnahan in 2010--probably a very good candidate in a neutral/better than neutral year for their respective party, but ran into a buzzsaw.
Poll
