The four different majors bring different prestige to different people. Other than being a major, the US Open generally brings two things to the table.
One: For Americans, it's always their national championship. Hopefully that's a pretty obvious statement.
Two: It's generally the hardest tournament in the world. Sure, there are exceptions to this from time to time, but the US Open generally takes that honor with room to spare.
As a matter of fact, it's often criticized for being unfair.
Regardless of whether or not it is unfair, some tournaments are just better than others. Generally a tournament's quality is based on how close it is, but strokes aren't the only factor.
Another tremendous factor is whether or not the players contending are big names. Is it two of the best golfers in the world going toe to toe on Sunday? Is it a real life golf version of Apollo vs. Rocky? Are there several players in contention on the last few holes?
Lastly, something that makes a tournament great is the lasting images that it provides. Some tournaments may play out in a very similar way, but one may lack that lasting image that the other one has.
Since 1991, four US Opens have gone to the 18-hole playoff on Monday. Of the 16 others that have been played, seven were decided by only one shot.
Indeed, the last 20 years has given us some phenomenal US Opens. It's also given us some clunkers, which is a very natural starting point.