When Under the Dome, based off a novel by Stephen King of the same name, premiered, it was an interesting story. But King had the luxury of telling it with the intent of the story being encapsulated within the confines of a book. He did not have to keep coming up with story to keep it going.
CBS on the other hand, had a bit of a hit on their hands and had to keep it going for what it was worth.
Sadly they covered the majority of the story of the book in the first season and burned through some potentially good story lines pretty quickly instead of letting them languish any longer. So they burned through the compelling content like a flash bang grenade.