I watched all three seasons of Defiance when it first aired, and then recently went back and binged it. I'm sorry to say it's not as good as I remembered. And the main problem I have with it is it's repetitive - something you might not notice when spread out over three years but is all too apparent when you watch the whole series over a long weekend.
Let's start with the good stuff - the show had a great premise, and they did a commendable job exploring it in the first season. The special effects makeup was better than average for the small screen, the cast was competent and the sets were quirky but plausible.
Where it fell short was the writing. They rehashed the same plot devices over and over again. I counted four separate and distinct subplots revolving around alien mind control tech. One or two maybe, but by the fourth go-round you'd think the characters would say, "Gee, Mary isn't acting like herself - must be more of that alien mind-control tech..." There were also three separate instances of characters having lengthy involvement with imaginary friends.
There were less obvious repetitions, too. The bad guys (and even some of the "good" guys) behaved despicably again and again - murder, betrayal, treason - yet two or three episodes later all is forgiven, and the bad guys are trusted members of society once more.
So in retrospect I have to say the first season was quite good, but by the second season it was falling apart and by the third it was a case of "been there, done that" to the point of mind-numbing predictability. A sad fate for a show that had so much promise...