We've never eaten in the restaurant; we always order it as take-out or delivery. The atmosphere is cute although a bit cramped. The dining room is somewhat small.
The food is good. I'd like to give it a 3.5 because it's just not a 4. It's not my favorite Thai place in Pittsburgh, but it is consistent acceptable. They are able to make things gluten-free, which as you know, is a requirement for me!
Beware: they are not kidding on the spices. For Thai restaurants, I usually order about halfway up the scale. However, I once ordered a "2", and it painful.
We like pad thai, the curries, the fried tofu, and the beef salad. We pass on the pad see ewe although pad see ewe is often meh when made gluten-free.
The prices are very reasonable.
TL; TD: Give Sukhothai a try for solid food, but don't expect to be wowed.