Having read this article: http://aht.seriouseats.com/archives/2012/01/blacows-in-tokyo-the-greatest-burger-joint-in-the-world.html
I decided to go to Blacows on my birthday while I visited Tokyo. I got the same Cheeseburger and fries that Eataku's writer ordered. Pic - http://i41.tinypic.com/jg605h.jpg
Was it delicious? Yes.
World's Greatest Burger? I wouldn't go that far.
Would I go back? Definitely.
They didn't ask me how I wanted my burger cooked so it came out medium. A bit more overcooked than I would have preferred. The flavor of the Black Wagyu A5 beef was amazing, but I felt the sauce they put on the burgers overpowered the meat a little bit. I definitely would go back to try it again, perhaps without the sauce. And for ¥1,100 (about $13) I felt it was a pretty good deal on a good burger in pricy Tokyo.
I will also say that the Wagyu Roast beef sandwich my friend got was amazing . Pic - http://i41.tinypic.com/21e69uw.jpg