I went to the midnight showing of Indiana Jones and the Kingdom of the Crystal Skull.  Overall, I liked it and thought that it was fun.  It was a little different than the other three Indy movies because it was more lighthearted in tone and it had less gore.  Crystal Skull definitely felt like PG-13 lite.  Harrison Ford, as expected, is awesome as Indiana Jones.  Both the story and Indy himself use Indy's age for laughs, so it's not too ridiculous seeing a character in his late fifties doing the stuff in the movie.  Karen Allen is great as Marion.  Marion last showed up in the first Indy movie.  Even twentysome years later, Allen just steps into the role very easily.  The character Mutt Williams is nicely done as a comic foil to Indy.  The villain Spalko is a fun Soviet caricature.

As for the plot, it is one that you either buy into or you don't.  The concept of the crystal skull and the mystery surrounding it are interesting, but the direction the writers take with the idea is one where you just go with it or you have trouble accepting it.  Apparently, George Lucas had mentioned seemingly off-the-cuff that he was interested in trying something like this, but I never suspected that he was really going to go through with it.  Also, I think one of the things that made the first three Indy movies compelling was that they only showed the power of the artifacts Indy was after, but not the actual sources, or creators, of the power and artifacts.  It makes everything more mysterious and engages the viewer.  In this movie, they do show the source and I think it does detract from the movie somewhat.  

The action scenes were a lot of fun, although the vine-swinging part was just totally over-the-top cheesy.  I do wonder if the filmmakers deliberately made it that way.  There was quite a bit of soft glow CGI lighting.  Several of the computer animated effects were nicely done.  Spielberg's action scenes have a certain type of quality, where staging action just seems to come to him easily and almost effortlessly.  His action scenes (in this movie and in others) always flow very smoothly and you can always tell what's going on.  There is always a sense of the action actually going somewhere, with one thing leading to another in a pretty detailed way, rather than a bunch of cool looking fight moves put together.  

Indy 4 was a fun night at the movie theater for me.  Even though the plot is buy-it-or-leave-it, I recommend seeing this movie.