Well, as it's been pointed out, it is NOT Disney-clean, nor Disney-nice, but the coasters are good.

Crowds depend on the day of the week, with (obviously) higher crowds on weekends, including Friday. I'd go on a Tuesday if I had a choice, however, it's likely you'll have fun even if it is crowded.
It is VERY hot though. I haven't been in awhile, but I recall there was very little shade, and I was miserably hot. And I live here - lol. Don't forget the sunscreen!
Will you be doing other stuff in Atlanta? The Georgia Aquarium is awesome, and the World of Coke is fun, and I think you can still tour CNN studios, which is right next to both those things. Also, Fernbank Museum (a natural history museum) is very cool. We had allotted 2-3 hours for it, and we stayed for 5. My kids loved it.
Have fun on your trip!