You're wondering if it's good, but you already have mixed feelings about it? I think it's terrific, great food without being too precious, and a warm room and atmosphere, though the service can be a little clueless, and it's REALLY expensive.
Mas is a lovely restaurant. It's comfortable, welcoming, and the service is among the best in the city. The food is very good, and the price is absolutely in line with the quality. They also allow BYO (corkage fee applies) which is great.
I ate there on Friday night. My skate was really delicious. My friend who wasn't so hungry ordered a scallop dish which consisted of 5 small scallops on the half shell for $18. The cheapest bottle of American red wine was $65! The wine at Per Se is more reasonably priced.