There are a lot of Indian restaurants in the greater New Haven area...plenty of them are good, few are great. If you're willing to travel 10 minutes outside of New Haven to Branford, Darbar has fabulous food and wonderful, friendly service.
The menu holds no surprises when it comes to offerings, but the caliber of the cuisine makes eating there exceptional. Of particular note - the saag (a dish that can easily be dull elsewhere is delicately and complexly flavorful at Darbar) and the Kadai Paneer (where the chunks of cheese, onion, and green pepper are never overcooked).
Don't overlook them for a larger affair - they have an upstairs room that is perfect for birthday/graduation parties, rehearsal dinners, etc.