The movie's star is its special effects. There is not much of a story at all: Earth is invaded by aliens, whose motives are not terribly clear. The only thing that is clear about these invaders is that they are ruthless. There is much spectacular destruction and death, and human resistance is futile. In the end the aliens are thwarted not by any act of humankind, but simply because the nasty critters, who have no resistance to earthly pathogens,
In other words, the effects are dazzling but the movie is not very interesting.
It might have been worth watching if the characters themselves had been interesting or even sympathetic; but we don't get to know the characters in the movie well enough to like them. Even if we had been given a chance to know these people, they don't develop at all. Cruise's character is mainly a jerk whose life seems out of control and who spends the entire movie running away, terrified, from the alien invaders. Dakota Fanning is cute but spends the movie simply terrified. The young actor who plays Cruise's son, who justifiably does not like his dad, is stuck with a role in which he is simply an impetuous adolescent. There was a chance that we might have found the father-son conflict interesting, or the reasons for the young man's seeming impulsiveness intriguing; but we can't hear any of the dialogue over the noise of the special effects.
Oh, well. Not a good movie-going experience. Maybe "Fantastic 4" will be better.