Indiana Jones and the Kingdom of the Crystal Skulls should have been called 60's sci-fi movie with Indiana Jones shoe-horned in.
The movie had many great action pieces, but there is more to Indiana Jones movies than action it is partially an attitude, and that attitude was sorely missing.
Everyone did well enough in their roles, but you really didn't care about anyone in the film, not even Indy.
The best way I could describe this to someone, is that if you disliked Attack of the Clones, you will probably dislike this movie, because it seems like Lucas wrote from a very similar place in both movies. Continual rehashes of previous action scenes, with almost no room for character...