I know exactly what you guys are talking about. I was like that too, it almost tarnished the entire movie for me when the aliens and spaceships showed up. But then I thought about it afterwards and realised that the movie had to just either end - game over. lights out. end of movie. or... something out of this world had to happen, which was what happened. The more you think about it, the more you have to agree that the ending was the only ending that would work! I mean, after all, you swallowed the part about the letter predicting all future disasters... If it had been an M. Night Shyamalan movie, it would have probably made it better cos you'd have known to expect something weird at the end...