I think everyone needs to cut the film a little slack. Continuing a franchise almost 20 years after its last movie is not exactly the easiest thing to do. It is somewhat foolish to expect a movie on par with the other Indy movies.
That being said, I had fun in the theater with this movie. The last movie I remember having fun at was POTC: At World's End.
Harrison Ford is showing his age, without a doubt, but I like how it was an integral part of the story. Shia LeBouf continues to surpise me, as his acting was good. Yes, I loved the monkeys. Monkeys don't often get a chance to be portrayed as decent in film (I.E. Night At The Museum, POTC). It was a fun sequence.
Cate Blanchett disappointed me. She's a fantastic actress, but she needs a dialect coach to get the Russian accent down. It sounded like she kept switching on and off between accents. She also needed a bit more development, aside from the whole "I'm a Paranormal Researcher working for the KGB."
The nods to the other movies were subtle (you get a cookie if you notice the Ark of The Covenant), and it was a fun experience.
I believe that this Indiana Jones movie did what it should do, and that is open up Indiana Jones to an entirely new audience, as well give closure to the older fans of the series.
The movie was enjoyable, and it does have its flaws but I don't go to the movies to see great acting. I go to movies to get lost in a world different than my own for two hours or so. Good acting is just a bonus in my alternate reality. While the acting was slightly below par, the adventure was out of this world (you see what I did thar?)