Block Island is good for beaches, seafood, biking, hiking, boating, fishing, and appreciating nature and the outdoors. It's not fancy. It's close to southern New England and New York, and there are plenty of ferries. No traffic lights, no chain restaurants, no highways.
No need to bring a car. Bring bikes, or just rent bikes.
Plenty of fun turn-of the century Queen Anne Revival (aka "Victorian") architecture. The island has an interesting history.
Photo below is from the town dock. Block Island is a popular sailing and boating destination.