I've been to a professional Murder Mystery dinner before, and my wife's been to Agatha's, and that's in addition to a couple of murder parties we've had with friends, so I hope our opinion holds some weight, but we really enjoyed this production. The actors were talented and high spirited. Then, from each table, a diner was chosen to act out a part, and a few of those folks were amazing (In fact, one woman - chosen to play a little girl - was so good that I thought that she was one of the actors at first). Now, concerning the dinner: you don't go for the dinner. Does that mean that the food is bad? Not at all. If you want a choice meal, go to a restaurant. Just remember: these sort of things are only as good as you allow them to be. If you allow yourself to be engaged and chat with your fellow diners and the actors, you'll have a great time, but if you want to be a bump on a log, then this isn't for you.
PS - About the Location - We went in early January and had no heating trouble. The facility, Blue Mark Studios - is a restored church and works well for large groups. Now, parking is on the street, but it was a side street, so traffic wasn't an issue. Finally, the area is industrial / commercial, not high-end, but far (very, very far) from the worst you'll find in Atlanta.