The fourth Indiana Jones movie is universally hated. What is the most commonly cited reason for this?
Aliens. That's it. Aliens. Sure, there are many other annoyances and defects often cited as well, but the aliens are by far the most common element to all complaints. In fact, it's the first and often even the only relevant thing that reviewers and other people mention.
Ok, then there's the fridge, of course, which is probably a very close second most commonly cited reason. (In fact, citing the fridge as a reason for hating the movie is even more irrational than the aliens.)
Let's put this into perspective and compare it to the original three movies. A supernatural chest that when opened releases some ghostly supernatural energy that kills everybody not worthy? That's completely ok. A secret cult that can, among other things, rip the heart out of somebody's chest with bare hands, while the victim remains alive through the whole process? No problems. A cup that grants eternal life? Completely normal.
But aliens? Nooooo! That goes too far! Aliens is way too much! And the fridge too!
What's happening here is a really strong case of nostalgia filtering. The people who complain about the fourth movie are mostly people who saw the first three movies as kids and loved them. It excited their adventurous imaginations. Now, as adults, they have these nostalgic warm memories of those times, when movies were wondrous escapes of reality into fantasy worlds full of adventure. Now as adults they cannot get that feeling anymore, and they are much more critical of movies. Therefore if a new sequel is made for the movies they loved as kids, they will be extremely critical and cynical about them. There's no way the new movie can grant them the same excitement and wonder.
If the fourth Indiana movie had been made back then, alongside the first ones, with all the aliens and fridges and whatnot, the attitude towards it today would be completely different. Today's adults would remember it fondly and consider it a good movie.
And conversely, if for example the third movie had been done now, people would hate it, even if it were identical. People would always find some ridiculous things to complain about.