Very well done. I’m not usually a great fan of sequels, but along with Star Wars, the Indiana Jones story is more like an epic saga, and this "installation" was done quite nicely and well within the Indy "theme."
They certainly stuck with a tried and true storyline. I won't spoil the plot with specifics, but as you'd expect, Indy gets called upon to help out his buddy by solving a mystery. He gets mixed up with some bad military guys. He decrypts the puzzle and saves the day.
There were quite a few interesting historical fiction references that I thought were quite clever. Again, I don't want to spoil the plot by being too specific, but keep your eyes and ears open for these sometimes subtle references.
Featuring a female nemesis was an interesting choice, and it worked out well. She was evil, but I didn't feel like I was meant to "hate" her. Shia Lebeouf also did a great job. His role stared out a little cheesy, but developed well.
There was just a little too much of that dramatic lighting at the beginning. The sort where most of the scene is subdued, and the actor’s faces are lit up a bit more in that silvery light. It’s an interesting effect, but Spielberg went a little overboard at first.