Well, after reading this in its entirety, my reaction is the same as that when I was sitting in the theater: What a weak screenplay.
A lot of people have wondered how Spielberg could have signed off on this, but if we want to be honest for a second, Spielberg hasn't exactly been the best judge of screenplays in the last fifteen years. A lot of modern Spielberg films are just a bunch of well-directed scenes that don't really comes together into a cohesive whole - I'm thinking of War of the Worlds (another Koepp gem) specifically.
I think what a lot of people have hypothesized is true - the long years of bickering between Spielberg and Lucas over the years was over story elements, and the priority of the writing even being serviceable got lost along the way. Lucas spent so much time insisting on a full-fledged 1950s Indy, and Spielberg spent so much time resisting, that the search for a screenplay just became about having enough of certain elements to placate both parties, everything else be damned. Koepp's script, I suspect, simply represents the first script that had enough of George's scifi stuff to placate him, and had enough traditional stuff for Spielberg to not be totally adverse to it. I really think that after all those years, Spielberg (and especially after the Darabont draft was nixed) just threw up his hands and said "Whatever, let's just make a new Indiana Jones movie already."
The irony of ironies is that Indy4's storyline isn't really that bad, but ultimately the story, which is what all this 19 year strife was apparently about, is a lot less important than the storytelling. You need excitement, decent characterizations, decent dialog, some kind of structure, and Koepp fails to to deliver on all of the above. This screenplay is a mess - an awkward hodgepodge of ideas that feel like they all originated from separate scripts, and likely did. That sense I got in the theater of just "watching scenes" that were just kind of there is one that revisited me when I read this script last night. It's interesting to see some of the things that got cut, and they're some lines in there I would have left in, but ultimately any such improvements would have been inconsequential - this script is the movie. The lack of any kind of thrills was still there. The completely bizarre pacing that makes the whole thing come off as disjointed is still there. The handling of all the secondary protagonists is as horrendous as it is on screen. And there's still no excitement. There's no "How's he gonna get out of this mess?" Where were the classic Indy escapes? And what interest the storyline could have offered (and what I think it still does on paper) is totally choked out by the languid way it's told - usually through clunky, weirdly placed exposition. agentsands77 nailed it when he said there isn't any real sense of intrigue. We don't care about anything that's happening in this movie. And the move is totally fine with it.
Koepp's script, unfortunately, is what I already knew it to be. Shame on Spielberg for caving in and doing a bully's homework.