It was all a bit 'by numbers' but I did enjoy it.
My only problem (ignoring technical innaccuracies
) was the alien's motivation - couldn't quite get an angle on it which bugged me a bit. But not that much
They were a team of scientists, scouts and explorers on a diplomatic mission and in search for a refuge for their people, who were being slaughtered by an enemy on their planet. They misinterpreted the U.S.'s probe as a friendly response to their S.O.S.
The U.S. was in the wrong from the start. For sending a probe and for attacking the aliens when they came.