Maryland. Mountains to the west, beaches to the east. If there weren't high taxes and a Baltimore there, it would rank higher than it does.
New York. Mountains to the north, lakes on the north west, a river valley running down the east, beaches to the southeast. If there weren't high taxes and NYC it would rank higher than it dies.
I live in NYC near Columbia University, work in a 100+story building and love New York (state). I would add that some of Long Island is fantastic, though coach covered that already referring to the beaches. I was in Riverhead a few years ago at the eastern part of Long Island where it splits into the north fork and the south fork. It was quite beautiful.
But I'm unsure that New York is underrated. My best guess or vote would go to Tennessee for the most underrated US state. It is luring many retirees and is one of only two states represented eponymously in the periodic table with Tennessine (Californium is the other element named for a US state though Berkelium is named for Berkeley, California).