a mile wide and an inch deep
Looks cool at first, but once you get to know them, they're as boring as a bag of old socks.
That new kid in class was amazing at first, but now he just talks about video games all day long.
My mom got a new job, and it looked great at first, but now she's stuck in a boring office with no friends.
The pizza place down the street was amazing until they started using mystery meat.