It's also not the first time he gets involved in unusual archaeology.
Amphibious Automobile: The so-called "Ducks" are actually scaled-up replicas of the Ford GPA/Soviet GAZ 46 constructed on modern jeep chassis. Replicas had to be used as the WWII originals are actually quite small compared to modern jeeps — small enough that a person standing on top of one could easily flip it over, making them too small for the fencing scenes. The misidentification as "ducks" makes perfect sense story wise as most people (including Dr. Jones, apparently) are not military vehicle historians.
Banned in China: Averted in Russia. The Communist Party of the Russian Federation tried to get it banned, but failed.
Creator Backlash: A little while after it came out, Shia LaBeouf opened up about his feelings on the film, expressing disappointment with it, saying he felt like he "dropped the ball on the legacy that people loved and cherished." The statement would later damage his relationship with Spielberg, who told him, "There's a time to be a human being and have an opinion, and there's a time to sell cars."
Creator Killer: This was the final major bump that led to Lucas selling his studio to Disney 4 years later.
Development Gag: Oddly enough the gag actually calls back to the development of Back to the Future — originally, the climax of getting Marty McFly back, well, to the future, was that Doc Brown was going to take him and a refrigerator to an A-Bomb test, and let the bomb's effects send him back to his rightful time. However, Spielberg was uncomfortable with the idea, concerned that kids might climb into abandoned fridges to play-act the scene, and so asked Robert Zemeckis to find a different approach, which he did once it proved too expensive to pull off. However, no good idea goes unpunished, as guess what iconic scene occurs in this movie?
Harrison Ford having aged somewhat since Last Crusade made setting the film in the '30s implausible;
But more importantly, after the harrowing experience of making Schindler's List in 1994, Steven Spielberg felt he could no longer use Nazis as disposable mooks given the enormity of their actions in Real Life.
Saved from Development Hell: It took 19 years for the film to be released, mainly because it took that long for Lucas, Spielberg and Ford to find a script they liked.
Technology Marches On: Somewhat inverted; to better match the previous three movies, this movie was filmed rather that shot digitally.
What Could Have Been: Early script treatments (from the 90's) supposedly had Indy communicate frequently with the alien, who would have had a name and a backstory.
In one of the treatments, Indy has a daughter instead of a son, which lines up with the original version of The Young Indiana Jones Chronicles before they were edited to remove all the "present-day Old Indy" scenes. (Natalie Portman was rumored to play Indy's daughter before the final project and cast was announced.)
John Rhys-Davies opted out of returning for a quick cameo as Sallah for the wedding scene between Indy and Marion at the end. As he tells the Onion AV Club:
"I guess it would’ve been rather sweet to be in that last little thing, and they did offer to bring a camera crew to me in order to film a bit of blue screen where you would’ve seen me clapping for the happy couple. But that’s all it would’ve been. I don’t know, I suppose I felt as though it would’ve cheated the audience just a little bit. I like to think the audience has some fondness for Sallah, and just to give him an appearance as brief as all that, a quick cutaway… well, that’s sort of short-selling him, isn’t it, really?"
Henry Jones Sr. was supposed to have a small role in the film but Sean Connery declined to return quipping 'Retirement is too enjoyable'; his character died between films as a result. His role most likely became Dean Stanforth.