I think that was one of the bigger problems of Kingdom that few have realized: The opening shot, the Paramount Dissolve, really sets the tone. In Raiders, it was unexpected, clever, and told us we were in for can-you-keep-up? sort of adventure. In Temple, with the gong and heavy music, we knew this was going to be INTENSE. And Crusade's Dissolve showed us we're back in familiar territory, sort of bookending a trilogy.
But Kingdom . . . whether it was a prairie-dog hole or anthill, our first impression is one of either "puny", "silly", "couldn't-they-think-of-anything-better?" or anything else to justify the post-StarWars-prequel-worries we all had. The first shot of a film, like the first line of a book, must GRAB you, but Kingdom's Dissolve seemed to just push us away a little bit, almost like Lucas and co. were saying "It's our movie, our way, like it or leave it". Not good.
Following that, people were inclined to be negative rather than enjoying the film. I believe this is where a lot of its (undo) criticism came from. Imagine if you can, forgetting all about Kingdom, and picturing a powerful Dissolve like the original three movies had, then play Kingdom out in your head. It'd feel different, wouldn't it?
But the fault is still Spielberg's. As director, he needs to remember the basics of showmanship, and joking with your audience to begin is not the best way to convince them of the drama and dangers to follow. Spielberg, with the prairie-dog hole, cast too light-hearted an atmosphere into this Indy film. Sure, there are thousands of different things one can nit-pick, but the first and last shots of movies are more important as they are your first impression and (supposedly) your lasting impression.
Maybe the Kingdom Dissolve could have been some unknown American ruins, something legendary to the Indians (and hinting at ancient civilizations having unknown--possibly alien--creators), where he and Mack were "digging in the dirt", then have the Reds show up, moving the Area 51 scene to after-the-teaser, superimposed over something else (like the Marshall College chase).