On a standard McDonalds Hamburger, the beef isn't that exceptional. Nor is the bun, nor any particular ingredient. But the diced onion, ketchup and gherkin are the trifecta of spice, sweet and sour (as muted as they may be). They work together in unison in such a way so as to give the Maccy Burger a very unique taste, and as such, it always irks me when someone asks for a "totally plain" hamburger.
Come on now. Surely that just tastes of dry.