It's telling that OPA! includes the word "fun" in their name, since the essence of Greek food is seemingly connected to some sort of celebration. People are (joyously) yelling things, food is getting set on fire (intentionally) and there's always some sort of shared dish in the middle for everyone to enjoy (your meal starts with complimentary hummus and pitas, which is a nice bonus). This is food intended to be enjoyed with friends, but even if you went by yourself, OPA! will provide a mood boost to go along with your meal.
Runners up:
2. Athens on Fourth Avenue
3. Fronimo's Greek Café