I'm disappointed in the Indiana Jones and the Kingdom of the Crystal Skull.
The older movies had a sense of weight, tangible in the sense of the journey that Indy undertook in each of them, and we went along for the ride. The series was full of action/adventure drama and mystical overtones owing to the various searches for long lost artifacts, but I think it endures because it speaks to the curiosity in all of us, the need to know about something Other (whatever your religion, or lack thereof). Another reason for the popularity of the movies is the sense that we could do what Indy does, that the adventures he embarks on could possibly happen in real life.
This movie is just another action/adventure flick full of ridiculous fight scenes that could not logically happen in real life, and the search for the crystal skull is full of mumbo-jumbo that makes no sense to anyone who hasn't looked into the eyes of the crystal skull and communed with the extraterrestrial being within. Sure, we're all curious to know how ancient people could have achieved what they did without modern technology, but the movie's vague answer, that "Knowledge," granted from the aliens, is the reason (with no further elaboration, other than a character saying "They have gone into the space between spaces."), coupled with the focus on flashy special effects rather than a journey that Indy embarks on, makes for an overall silly movie that should never have stooped so low.
An interesting review over at Books & Culture: Indiana Jones and the Deadly Blather