There was a Spielberg SF spoof in which the superimposed cartoon aliens wound up killing everyone (including Jack Nicholson in his role as President of the US, if memory serves). That sucked. There was an amusing movie in which some alien gang that couldn't shoot straight tries to conquer the Earth, but alas arrives on Halloween, so no one will take them seriously. Can't remember either title.
The Jack Nicholson film was Invasion of Mars. I saw the other film, but can't remember what it was called, either.