I would like to see this series at some point, surely, though it's too bad the whole thing is unresolved at the end (or so I've been lead to believe).
It wasn't the norm for any show back then to be resolved at the end. Gilligan never got off the island, the Robinsons never got un-lost in space, the Spindrift crew never got away from the land of the giants, etc. The Fugitive was a rare exception.
And really, The Invaders didn't have that much of an arc anyway. I talked about that in my blog review. It did have a certain vague element of continuity to it, with Vincent gradually learning more about the aliens and eventually, in season 2, starting to gain allies, but for the most part it was extremely episodic and had minimal continuity or progression of any kind, just like most shows of the era. So there wasn't much to be resolved.