These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Indiana Jones and the Kingdom of the Crystal Skull
Broken Base: Reviewers, fans, casual viewers, all possible groups are split!
Contested Sequel: It's hard to pin down a specific ratio, but opinions are sharply divided over whether it's a worthy follow-up to the original trilogy or not.
Critical Dissonance: Critics generally enjoyed it, while fans seem to loathe it. On Rotten Tomatoes, the audience score is lower than the critics score.
Fanfic Fuel: This installment definitively establishes that Indy was an active OSS agent for the entirety of World War II proper note The main trilogy takes place in the years just prior to the war, and that he spent around a decade spying against the Soviets with the CIA during the Cold War. That's around seventeen years of undocumented high-stakes adventures.
Fanon Discontinuity: Since this is to Indiana Jones fans what the prequels were to Star Wars fans, a lot of Indy fans like to pretend this film doesn't exist.
Inferred Holocaust: The tribe that lived near the temple most likely were killed by the departing spacescraft or drowned by the river flooding the valley.
At least, any who remained after the Russians gunned down all the tribesmen who were guarding the temple, as shown on-screen.
Mis-blamed: Lucas gets blamed for the decision to make Soviets the villains rather than Nazis like in the previous films. In reality, due to the harrowing experience of making Schindlers List, Spielberg felt he could no longer make movies featuring Nazis as simply stock villains, although Harrison Ford's advanced age since the previous film also accounted for it.
Narm: At the end Indy says the secret Mayan treasure was knowledge. "Knowledge was their treasure." He says this with a big stupid grin on his face while the cast looks directly at the camera.
The original 1982 Back to the Future script featured Marty McFly surviving a nuclear blast in a fridge-time machine, in order to return to the present. This was scrapped because it was too expensive to pull off, and there were concerns that kids who watched the movie might climb into abandoned refrigerators to "play Marty." If that sounds at all familiar, it's because Spielberg was also executive producer of that film, and also used the idea in an earlier version of the script in the earlier years of the franchise that was later adapted into this movie.
One True Pairing: There is one aspect of this movie about which pretty much everyone can agree, and that is that Karen Allen's return as Marion Ravenwood is FUCKING AWESOME.
The Scrappy: Mutt, to some people. It doesn't help that he's played by Shia Labeouf.
In fact, practically every brand new character introduced in Crystal Skull is hated for little reason beyond being in Crystal Skull.
Special Effect Failure: The prairie dogs, the monkeys and the aliens have been derided for this. The chase scene in the final act utilizes a good deal of green screen.
They Changed It, Now It Sucks: A common complaint of its disappointed viewers. Some long term fans criticized the heavy emphasis on CGI for many of its action set pieces (and in general) when the original trilogy was famous for its now iconic stunt work and great use of practical effects alongside CGI. Others feel the shift away from supernatural/fantasy elements towards sci-fi and aliens was a move too far.
They Just Didn't Care: Like the Star Wars prequel trilogy that came before it, this long delayed 4th Indy film is often bashed due to the writing, which is viewed as so inferior to that of the first three films that most fans and critics just can't shake the feeling that no one really cared about the film while working on it.
They Wasted a Perfectly Good Plot: So much could have been done with examining how hard it would be for Indy to still have adventures at his advanced age, but the final product feels more like an excuse for Ford and co play out their older guy hero fantasies.