tl;dr: A manga with interesting themes, characters, and plot threads that just throws them all away at the end.

Zetman is to some degree a manga about super hero origins, but it's more so a manga that explores some of the issues relating to the ethics of super heroes, and hence goes deeper and gets quite a bit darker than most super hero related works. This dark setting works pretty well, and the issues relating to justice and such mostly come through pretty well. The various character relationships were done pretty well too, with Jin and Kagou serving as good foils to one another, and the romantic aspects also being pretty well done for the most part. The plot was interesting too, in that there did seem to be a lot going on and a lot of players with various motivations and plans. However, all of this is severely hampered by how the ending is a complete nonending that doesn't do anything that an ending is supposed to do. While the ethics and such behind being a hero and justice were explored a good amount throughout the series, in the end it never felt like they actually made any sort of point. The various character relationships too end on a note where they're all completely broken, which is simply sad, not bittersweet, just kind of bitter. The plot never actually comes together. There are a lot of plans and conspiracies and twists where it turns out that the plans, goals, and motivations behind various characters are very different from what they appeared to be, but in the end it never became clear what the actual goals were, and what was actually going on, and ultimately the extremely long finale simply felt like chaos. There isn't a proper ending, rather the ending is essentially a set up for a time skip, being more preoccupied with setting up new plot threads then resolving them. But even in terms of that, it felt quite strange, in that it doesn't stop at the time skip, but has one chapter that shows things after the time skip that doesn't actually resolve anything either but rather just feels kind of awkward in terms of there eventually being a proper continuation. Though considering the time frame, it seems unlikely a continuation ever will be made at this point. I really liked the art style, art, and character designs, though I was fond of the general style more towards the beginning toward the end because it seemed it got a lot more reserved.