If you do check out Extant you should lower your expectations as low as they can go, I don't really have standards (I like Falling Skies for crying out loud) but Extant is below my threshold for sustained viewing. The whole thing, from the set design to the overall story, feels like it jumped out of the imagination starved brain of a baby boomer desperate to shape a vision of the future that'd be "cool".
The biblical overtones really aren't helping its case, Under the Dome manages to be subtler.