From what I saw, Jason Ritter's plotline was too tangental to the core alien-invasion story. But you need to have a character like that, the everyman, who the audience can relate to. The sleeper agent guy in the FBI could be the other lead character.
But the problem still remains: what is
the story about the aliens and why should we care? All I know is that they apparently are trapped on Earth and are a bit surly about it, and planning to do something about it. Is there anything more to it than that?