I've had a "Mega Mac" before, at a McDonald's in Taiwan in 2007. If a regular Big Mac has two patties and three bread/buns, that Taiwan Mega Mac had three patties and four bread/buns. This 2013 Japan version has four patties and three bread/buns! And it's yummy!
It was difficult to eat though, compared to what I can recall from my experience with the 2007 Taiwan Mega Mac. There was a Japanese to my left who also ordered a Mega Mac and he was sitting comfortably with no Mega Mac in sight, as if he had easily conquered the Mega Mac and I didn't. I felt "insufficient," but I consoled myself with the thought that it's a skinny Japanese guy who's the hotdog sandwich eating champion for a number of years. It turns out that he had asked his wife to ask for a fork for him -- ha, I won that round! Hehehe.
McDonald's also has this promo -- they serve you in 60 seconds or you get a free Big Mac. This is only for orders between 11:00 and 2:00pm. They were a little too kind, too. I thought their hourglass timer wasn't up yet when they had given me and the person in front of me a coupon each. Anyways, their "campaign" ran only until last January 14, I think.
But... Okay, McDonald's Japan. You got me at "free." I'm coming back every week. :D
By the way, for some reason, I like the Quarter Pounder more than the Big Mac, but I seem to like the Mega Mac more than the Big Mac. I think it has to do with meat-to-bread ratio. The Big Mac is too much bread for my taste.