I have reread this series for the third time, it's more amazing than ever after I have reread a few other shounen series like One Piece, Nanatsu na Taizai, Onepunch-man, Boku no Hero Academia and so on.
I like this series because while there are inconsistencies here and there like Ageha's powers and personalities (yes he too has the sudden power up syndrome) and the ever existing time paradox, the series is quite progressive (and also a bit draggy) in showing the aftereffects of the present contributing to the future. And more importantly, in a shounen series, normally romance is not touched so much upon, but this series not only progresses the main characters' romance, the side characters' romance, but even for the villains. The author is simply amazing in storytelling, no doubt.
Some reviews say the ending is rushed because it was axed, well I am amazed. It is still so amazing, I can't tell that it was rushed or axed. Look at Mx0 and Double Arts for reference.
Regarding the originality of the series, it does feel very Gantz-life in the beginning. But Gantz's story is very messy and initially, the first MC is more like a villain than a protagonist. But Psyren does this right from the beginning. And expounds on it with the plot following from his initial intentions and behaviour, before expanding into more plot. In this sense, the plot is really progressing from his one single action towards the end. And along the way, it also branches into several common shounen scenarios, such as friendship.
Overall, I would say this is a great series, I love how most of the characters have distinct personalities that further the plot naturally, rather than incident-based. A series I find it similar in this aspect is Angel Densetsu, even if the genres are very different.