Oh dear. Where to begin? To say that the title is something of a red flag is a serious understatement. If the writers can't come up with something better than "Teenagers from Outer Space," then how good can the movie be? The answer is not very.
The movie starts promisingly enough, with a shaggy dog running along and barking. Everyone likes dogs, right? Well, apparently not everyone, because when Fido starts barking at a fake looking saucer, the hatch opens and a masked alien shoots him with a ray gun, instantly turning him into a skeleton. The alien then removes his mask to reveal- a human. Yes, what better way is there to save money on costumes than to have the aliens look like regular people in weird clothes?
It's soon revealed that these space teens have come to earth in hopes of using it as grazing land for their livestock, the grecken. A fight immediately breaks out. Derek, one of the aliens believes it's wrong to unleash the grecken on a planet with intelligent life, and is willing to hold the others at gunpoint to prevent that from happening. Through some incredibly wooden dialogue, we learn that on their home world, they have no families, and that the old and sick are killed off to preserve their "Supreme Race."
Well Derek makes a run for it into town, and one of his shipmates pursues him, while the others head back into space, and the grecken is left in a nearby cave. O and I forgot to mention, Derek's father is the Supreme Leader, an important tidbit that didn't come up until Derek had fled.
So Derek ends up boarding with a nice family through a series of highly unlikely misunderstandings, and his pursuer stays one step behind him, vaporizing anyone who seems to be getting in his way. There are poorly staged shootouts, dull car chases, and of course the hero finds a nice girl who repeatedly ignores his instructions to stay out of danger.
And even when the trigger happy villain is thwarted, there's still the grecken. By this point, you're probably wandering to yourself "just what is a grecken?" It's a lobster. And not just any lobster, it looks normal at first, but after a day on earth, it's as big as an elephant... and hungry for human flesh. The scenes in which the hero battles it are among the most ridiculous ever to appear on screen, because even a five year old can tell that someone's just projecting the silhouette of a crawfish onto the screen. It doesn't even look like it's walking, it just kind of floats around, wiggling its legs.
You've surely guessed by now that the acting is as abysmal as the effects. Every line is stilted. I'm not sure if the aliens ever use a contraction throughout the film. These guys have about as much personality as Microsoft Sam. And the townspeople. If you were approached by a man in a Starfleet uniform, ray gun at his side, who had never seen a car before, wouldn't you have a sneaking suspicion that something was up? But these folks don't seem to notice anything funny until the ray gun's pointed at them. I don't know, maybe they're relatives of whoever wrote this mess.