TL;DR: Really good world creation, really good character creation, and absolutely terrible interpersonal writing that manages to waste everything that is really good about the world and characters for the sake of vicarious, self-gratifying wish fulfillment for those who long to be the unmatched center of attention and object of all desire.
FULL REVIEW WITH CHARACTER DEVELOPEMENT SPOILERS. DO NOT READ IF YOU WANT TO SIMPLY ENJOY YU-NO: The world and overall story of YU-NO are creative and interesting enough that I really want to like this anime...I just can't. The sad truth is that when I compliment the story, I am only speaking of the macro-scale story; the overall concept and mysterious hidden truth of YU-NO's worlds and timeline. When it comes to the dialog and developement of the characters, every character is condemned to exist in, and be concluded with, some of the most predictable, boring, and childish writing I've seen in many years.
Is the character a male other than the main protagonist, Takuya, or the villain? Then the character will be an inconsiquential and unappreciated beta-male that exists to be:
A. "the loveable screw-ups who mess things up time and time again."
B. "the background filler characters that make the world look populated."
C. "the victims who prove the severity of the risks by suffering or dying to make that point."
D. "the unrequited love interests who show us how hopelessly fixated on Takuya almost every female character of significance either is or will become as the story progresses."
Is the character a female? Then the character will start off with interesting motivations and background, but will inevitably:
A. "become a hopelessly, emotionally attached love-interest of Takuya who either gives into belonging, heart and soul, to Takuya or spends the rest of her time in the anime as an object of sexual tension that proves to us, the viewers, that Takuya clearly is just that desireable to all women. This leads to that female eventually dying or being permanently whisked away as a dramatic and tragic motivator for Takuya with their final moments being vulnerable, emotional moments of deep personal connection to Takuya."
B. "an unrequited love-interest, left behind to pine for Takuya as the one whose love they will continue to long for while contending with only lesser males for the rest of her life."
...and once either female's story has reached it's emotional conclussion, Takuya simply gets on his way toward the next swooning female for the writers to trivialize. NOTE: There is one female exception to this rule, arguably two. Inevitably, though, any female character is doomed to either die as emotional fodder or be left behind, never to know the love of such a perfect being as Takuya...
I've certainly enjoyed "OP main character", "harem" anime, but the "everyone falls into one of these exact character developement paths" treatement ruined otherwise good characters and the deeper, big-picture story of YU-NO for me. The love fixations were completely unessecary nine times out of ten and the characters could have been allowed to exist as more diverse, emotional losses to Takuya as comrades who fell tragically along the way without the tired repetitions of "and now she's smitten before, oh no, tragedy for Takuya again".