We LOVE Atlantis.
My husband and I have been dining at Atlantis since at least 2007. I lived in Chicago most of my life, and the food at Atlantis is as good as the best restaurants in Greektown. (But we haven't eaten at Plaka in Madison, which is "closely related" to Atlantis.)
I'm a vegetarian and Atlantis offers a ton of great veggie choices - not always an option when you're outside of Madison proper. The hummus, Spanikopita and Squash pie are all amazing. My husband loves the olive stuffed meatballs. The prices are incredibly reasonable, and the orange cake is a fabulous way to end your meal.
Atlantis has a reward program too, so if you dine there with any regularity you can save some on your meals over time. They also do special small plate events every so often, which give you a great chance to try a lot of different dishes.