^^ Yeah, I've gotten in the habit of staying through the credits everytime I go to the movies, just in case.
I read a post on another board arguing that the aliens' apparently stupid actions make perfect sense if you assume that:
a) The "attack" was really a crash-landing caused by accidentally clipping a satellite on the way down.
b) The aliens spend most of the film acting in self-defence and are actively working to minimise casualties.
c) The real bad guy is the human protagonist, who continually escalates the situation with his deranged over-reactions, and who only comes out looking like a hero because his actions manage to get his commanding officer killed, leaving no witnesses to the fact that he exceeded his orders and opened fire without authorisation.
Haven't seen the movie, but its an interesting alternate take.