I was actually a little disappointed in this conclusion.
First, let me say what it does do well. It is pretty faithful to the original in style. Infact, its pretty much just a continuation of 20th Century boys. It doesn't try to deviate from the formula, but thats not a bad thing. It also does add a relatively satisfying ending and it closes off a lot of the mysteries.
But, it doesn't really live up to the climactic conclusion that I would have liked from 20th century boys. Really, I think the ending to 20th century boys was full of more emotion than the ending to 21st century boys. This was more of a "filling in the holes left by the real ending". Also, the 2 volumes seem to spend too much time doing where are they now and trying to make the reader realize that all the characters are still there. I mean, theres only 2 volumes, yet every still living character that was given a name and introduced in the entire series was given some panel time, and some of it just disrupted the flow. I'm tempted to say even all of the dead characters made an appearance.
Lastly, the series seemed to spend too much reliance on psychic powers. It makes it feel a bit contrived and forced, and is quite a deviation from the original series. I'm not saying that 20th Century Boys ever tried to be realistic, but although it bent them a little bit, it tried to stay within the same laws as the real world. And the lack of psychic powers is part of the suspense. Because it gave the idea of "How did he do it?" or "How did he know it?". But when you throw psychic in, it just kinda throws logic out the window.
But overall it wasn't a bad read. And is definitely worth reading. If only to fill in the holes. I just feel it could have done a lot more.