I'll be the Indy apologist.
I liked that movie just as much as any of the other Indiana Jones movies...which is to say that I enjoyed watching it a lot. It's not without it's flaws (I'm looking at you "leboof"...swinging around all Tarzan-like), but none of the Indiana Jones movies are flawless. When compared to the older films it's clear to me that "Crystal Skulls" shares the rhythms, over-the-top action, and goofy sense of humor.
...actually... Now that I think about it, I really liked this movie.
I wonder if most of this film's criticism comes from people forgetting what the originals were like to watch. In the many years since they were made, the action genre has had so many renovations that the conventions of the Indiana Jones movies end up seeming quaint 15 years down the road.