As a fan of the Big Mec, but not an often eater of it, everything about it other than the airy brioche bun is heavy. The patties (which I love personally) are not huge, but definitely larger than an average fast food type burger, and are seared rare, there seems to be quite a bit of beef to contend with on the double burger just to kick things off, lots of "juices" flow from the patties, which are actually literally chopped steak (bifteck hache) as opposed to ground beef.
Those fatty juices meld with two rather intense sauces, a foie gras red wine bordelaise that is quite luxuriously thick and fatty (though it has some cut from the almost balsamic notes thanks to the red wine, but given its reduction status it's almost adding more of a sweetness on top of the foie gras plus the bone marrow, shallots, and butter common to the sauce). Then there is also something like caramelized onions interpreted as a viscous reduction of French Onion soup. A hefty smear of garlic aioli , and two slices of melty, thick, funky American cheese that get melted into goo by the chopped steak juices.
The burger is sort of an onslaught of richness...there are effectively THREE rich sauces (bordelaise, aioli, and reduction), plus a good amount of gooey cheese layering two juicy steak patties...
It's QUITE an experience. I could see how it would be too much for many people. For me, I found that it's really messy and intense, and the flavors do somewhat congeal, but, for me, into the sort of ephemeral magic that Carl's Jr. commercials promise in a burger eating experience (but never deliver).