George Lucas wanted the story exactly his way and even going as far as rejecting a script that Spielberg thought was well written and entertaining. However, Lucas always wanted to shoehorn in an Alien plotline into the Indiana Jones series. Spielberg took the idea and grounded into making a bit more sense than what Lucas wanted. Both Ford and Spielberg thought Lucas’ idea was too out there, so they toned it down a bit.
The alien plotline really does hurt this film a lot. While it does fit with the strange supernatural stuff from the first movie, real life aliens seem too X-files for an IJ movie. However, the entire subplot about Indiana seeing the passage of time is a nice touch and should have been
The dialogue ranges from flat to unexciting. You can tell Lucas got his hands on the script and did some rewriting. Not everything is doom and gloom in the story, there are some good continuity moments in this film that are nice little call backs to the older IJ films. (Look for the Ark)
Lucas should have stepped aside and let the writers and producers do the movie they wanted. And as far as plots go, the first and second acts work very well. It is toward the end that the movie falls completely apart with all the Alien mumbo-jumbo.
The Overall Picture
While not a complete disappointment, Indiana Jones And the Kingdom of the Crystal Skull isn't the best movie in the series, but certainly better than Temple of Doom. It is still a fun action/adventure movie that should be watched if you're a fan of the others. It's a good movie, but not as fun as The Last Crusade or as creepy as Raiders of the Lost Ark. Yet, there are things to enjoy and it is still an Indiana Jones movie.