Based on my few visits - Quite okay. I always walk in and don't use the drive through and don't go during peak hours so I've never had any significant wait. My doughnuts and coffee have always been satisfying, if not particularly exceptional. The interior has been clean on all of my (few) visits and staff has always been pleasant, and there's free WiFi as well. It's just a Dunkin', and not exactly "the Starbucks experience", but I'm okay with that.
P.S. Tried and liked several of the (new?) croissant sandwiches.