Unlike cold fusion this has been duplicated at least 3 times. And NASA even tried to break the system deliberately and it still worked meaning they really have no idea how it works. I'd say with 3 successful independent tests by some very smart people and we've got something interesting even if it turns out to be worthless as a propulsion device. They are going to be writing papers about this for years trying to understand the effect and it's nuances. They might have discovered some new aspect of the universe we didn't understand, or they could have simply discovered that taking measurements on a device like this is problematic.
Just goes to show there are so many areas we've just barely scratched the surface in. Even if this isn't some amazing new propulsion device it's possibly going to reveal something about EM radiation we didn't fully understand. Either way it's pretty cool IMO. It's not often you run into these situations where you can basically stump some very smart people with something that shouldn't exist. Cold fusion might have ended up being nothing but a chemical reaction but out of the gate that was pretty obvious as no one could duplicate the results. This has independent confirmation to at least some degree.