This is really just the end of the 20th Century Boys manga. I think the name is cool, but it would make more sense to still call it 20th Century Boys.
How was it? It was interesting and it wraps up the loose ends, but not as good as the first 250 chapters.
Not nearly as sublime as the uncannily sublime 20th Century Boys (2 volumes compared to 22 but shush) but a solid follow-up nonetheless on one of the most magnificent and unbelievable works in manga ever. You fall into two camps: The first one, the uncultured heathens who haven't read 20th Century Boys, and the second one, those who have walked the path of Kenji and Friend. First camp, leave this page and begin reading. Second camp, this is the grand finale of the series. It wraps up the saga of Friend, the Kenji Faction and all inbetween. As a conclusion, it does a fine job all things considering and is a must-read to get the rest of the tale. Sure helps if you read it right after you finish 20th Century Boys so you wouldn't be forgetting anything but for someone like me who read it months after the final volume of the saga before it, it still went pretty smoothly.
Know what? Even if you only liked it, you should read it. It's pretty much volumes 23/24 and if you stuck through the first twenty-two, you should stick with it to the very end. Completely worth it.