Lowered expectations helped a lot. The first half of the film was very entertaining. People in the theater cheered and clapped our hero's return. Indy actually says "nucular". Nice touch.
Some critics seem not to have enjoyed Shia Leboeuf's entry in the story. I thought it was cute. Not many 12-year olds will recognize a reference to "The Wild One". The 19-year olds sitting behind me struggled with Shia's name. I thought that was funny. (And not so funny? What the screenplay does with the two lead characters - Indy and this kid. Other than the obligatory comical bickering and some mild antagonism, there was just nothing between them. A huge lost opportunity, story-wise.)
The second half of the movie was not engaging enough. There was definitely a sense of restlessness among the audience. Imagine, there we were, watching a new Indiana Jones movie and a couple of idiots in the crowd (from a certain Ivy league college) were busy texting. No, I don't think the problem is lack of attention spans at all.
There is a lot happening in the second half but, and this is the real problem, I was hardly paying attention to Indy. There are too many characters filling up the screen and they are mostly uninteresting.
But the definitely-not-as-cool-as-melting-faces-climax and the closing sequence can still be enjoyed.
Just lower your expectations. A lot.
Someone on Digg commented on this movie: "definitely did not suck as much Phantom Menace". Nowhere close. Indy fans got a much better deal than Star Wars fans.