It's pretty good, but several things kind of keep it from the top of my list.
The multiple world resets, 'faulty memory' being abused like crazy for plot devices, psychic powers, and the existance and use of the New Book of Prophecy all irk me the wrong way.
That said, it's still does what it does fantastically. Suspense, action, mystery, humor is all handled exquisitely. The characters are likable and, for the most part, believable. Art is wonderful and distinctive as expected of Urasawa. Even though the plot runs though some areas disagreeable to me, the story is still ambitious and arranges itself well for a story of such grand proportions.
Vastly superior to most everything else you'd read.