It's only afterward that you realize how preposterous and vacuous it actually was.
Point one: the first thing the arriving aliens tell us is that they have only come to Earth to get one resource which they have exhausted, and that once they replenish that, they will leave, and in return they will give us technological advances.
Well, here's the kicker: that missing resource turns out to be aluminum foil for conical hats.
Or perhaps it was dryer lint. Or CD copies of America's "Horse With No Name."
In fact, we are never told what the resource is. The entire plot point is never mentioned again.
Point two: one of the first things we say to the aliens is "our scientists say that it's impossible that you look exactly like us" (which they do, only better). To which Anna (Firefly's Morena Baccarin), the alien's gorgeous leader, replies curtly "Our scientists can explain that."
And their explanation is ... they've eaten so much dryer lint and listened to so much America that it has transmorgified their hideous alien physiognomies into the cast of America's Next Secretly Reptilian Top Model.
In fact, this plot point is never mentioned again, either. I think we're supposed to think that the aliens have offered their explanation and that our scientists have been duly convinced, but that's preposterously bad storytelling. You can't leave their explanation out; their explanation is our only justification for trusting them.
And of course the only conceivable explanation is that we share the same origin. In which case, they are not alien visitors, they're essentially us. And everything we think we know about human evolution is wrong. Both of which would make thought-provoking plot angles (as alien lies we were led to believe), if the show had any interest in provoking any thoughts other than "that makes no sense whatsoever."
(Note that Philip K. Dick's Now Wait for Last Year has this same idea; aliens from the planet Lilistar have arrived and, playing on their status as our secret progenitors, have enlisted us in their war against horrible bug-like aliens. Of course, there is a delicious PKD twist which I shan't reveal if you haven't read what is widely regarded as the best of his non-famous novels).
Point three: everyone calls them "the Visitors," or, for short, "the V's." No one has asked them what star system they come from? They haven't told us? No one cares? And when was the last time you heard someone call the Iraqis "the I's" or the Russians "the R's"?
Point four: it is ultimately revealed that many prominent humans in positions of power are secretly aliens, and that this is part of their plan to exterminate us. Showing up over all the Earth's cities in huge spaceships, Childhood's End style, is just the next phase in the extermination plot.
WTF? WTFF? Why didn't they just wipe us out when they first arrived here twenty or thirty years ago? What is their rationale for going to all the enormous difficulty of cloaking their hideous reptilian alien physiognomies in the faces of mostly obscure Hollywood actors, and then providing us with universal health care?
Now, if it weren't for points one through three, I might hold out for some ultimately satisfying explanation for what the aliens are up to. If that happens, I will buy the first person who notifies me of such (and provides a good argument for the storytelling worth of the explanation) one copy of every item of the show's merchandising tie-ins.
In the meantime, though, we have a show about an alien invasion where the alien's ostensible purpose here is omitted, where there justification for earning our trust is omitted and / or preposterous, and where their true purpose is preposterous.
Other than that, it was really good.