Another blogger summarized the movie like this:
Raiders of the Lost Ark was the best of the series. That aside, I can summarize Indiana Jones and the Kingdom of the Crystal Skull in three sentences:
• Indiana Jones meets the space aliens.
• An army of ewoks/monkeys comes to the rescue.
• There is a flying saucer at the end.
So if those three sentences don’t bother you, you'll love the movie.