There are several contributing factors to the 3-starness of Papaya Thai, but it isn't necessarily the food. This place is literally a block away from my house, and I have ventured frequently because of its proximity, reasonable pricing, and portioning.
Giant fish tanks with some cool tropical fish are strewn about, but then there is this tank with the ugliest eel-like fish and catfish. It makes it hard for me to eat looking at them, so I opt for seats facing the opposite direction. I also feel like there are too many tables for the amount of space. If the restaurant where ever full, I think I would knock into someone's head with the imaginary purse that I do not carry.
Now onto the food. I love that there are spiciness scales that I do not adhere too. I always ask extra, extra spicy, and they don't just throw a handful of red chile flakes into the dish that I order. Every curry dish I have ordered has tasted the way it should, not like coconut milk or peanuts. The price isn't terrible for the portion. I always have enough left over for lunch the next day. Try it out.
P.S. I think they are under new management since my last visit.