It's great seeing Monster on the page, as I finished watching the anime not long ago. I actually really loved the conclusion, as it wasn't so much high stakes as it was a clashing of the various themes that were threading together. Plus Nina's line is one of my favourites in the series.
Few spoilers here that I discuss:
I always had a similar view to the "scenery of the doomsday"; it was isolation. To me that was why Roberto couldn't see it, he had nothing to lose as he had no memory. Johan still cared for his sister in a twisted way and remembered all the loss in his life as he became alone. Tenma felt at that moment that he was losing everything and that there was no one for him.
End spoilers.
I have to say I do hold a big grudge against Monster though. For me it was so amazing that I just can't take the majority of (mostly modern) comics seriously now. Their constant resurrections, almost zero themes and wildly alternating characterisations that often butcher what the previous writer did has made me tired. And the status quo, oh God the status quo. I only buy select DC comics now.