Now that's a movie. Damn fine movie. Enjoyed it quite a bit. It's no Citizen Kane or Robocop but still very enjoyable.
I don't think it was necessary for the aliens to keep getting worse in the things they did. Seemed like Spielberg felt like in order to increase the tension or the scariness of the aliens, he had to keep one-upping himself. For instance, I don't think the eating humans thing near the end was necessary. He could have found other ways to increase the stakes. Also, the part with the grenade there? Saw it coming a mile away.
In a lot of ways, the movie is predictable, but it worked. For instance, near the beginning when the aliens begin attacking, Cruise' character stands around like a gawker. Because we know bad things are coming, we're all thinking,
run, you moron! I think Spielberg counted on that reaction a bit. He counted on that so the audience' frustration with the characters would build up, the more to make you think they would be so dumb they would get themselves killed. Nice way to build tension.