Superpowers are usually a metaphor for the power of adulthood, independence, agency, prospect of change in oneself or change in the world. In The 4400 they were a metaphor for political power for those who didn't have any and the hope of social and economic change making a new world, the kind of place usually dismissed as a utopia. The word "revolution" was openly invoked. It wasn't an accident that an episode was entitle "The Great Leap Forward."
Most TV and movie scifi is adamant that things should not change. The 4400 was unusual in that some of the characters were allowed to think differently. That makes it different from the likes of Mutant X, Alphas and The Tomorrow People (so far.)
There were some problems. They kept ratcheting up the stake but never progressed toward a resolution. And like so many writers who favor character stories, they frequently bungled character. One of their finest episodes "Life Interrupted" showed lead Joel Gretsch in a years long relationship. Then, for whatever reason, the actress Karina Lombard left, Jenni Baird comes on board, and years of marriage are ignored. And I get tired at how many times they exposed Billy Campbell as bad, then showed him as good. Patrick Flueger must have gotten dizzy trying to remember when his character was on good terms with Campbell's or when they were at odds.
But over all, the willingness to even admit the very prospect of change, even with the caveat the heroes would win in the end and undo it all, was very striking.
As to the post-finale novels, I must say that Greg Cox did a superb job keeping the characters true to their TV selves, and in voice. (One quibble about the April Skouras character.)
The Mack I'm afraid seems to develop the plot at the expense of the characterization. Then in the final paragraphs it opts for a final resolution to the choice between the past and the future, opting inevitably for the past. But it does so by a voice from the future announcing that the events of the novel were all a mistake. No, there is no clue how events are to be undone.
If this all seems cryptic, I'm trying not to spoil things for any who might find the novels.