Short-Review for those who just want Quick Overview:
Story (8/10): Will hook anyone interested in crime-solving stories within 2 episodes, Very serious and emotional with the overall theme of child abuse but also about self-discovery. Otherwise It has really tremendous (especially visual) Storytelling (one of the reasons why it was so hyped). Don´t expect MC´s Time-Travel Power to be explained, it´s just a MacGuffin. The Ending is maybe not what you expected but again very well executed and will most likely leave you satisfied.
Characters(8/10): Every Character has a uniqe personality, zero stereotypes and the best Character Depth you could have within 12 episodes, although it could have been even better with one or two episodes more - Manga is recommended for this.
Animation(7/10)/Sound(6/10): Awesome OP/ED, good OST but with a few pieces too little. Nothing groundbreaking in the Animation Department, astonishing use of Colour and Cinematography.
Summary: As good as Anime gets within a 12 episode Series. If the you are touched by its serious theme, you will love it for the feels and will oversee some weak points through it´s great visual Storytelling. If you were looking for a murder mystery with a timetravel twist or heard of it as the best anime ever, you´ll most likely be dissapointed.
Personally Opinion: The Anime I enjoyed the most last Year. I got really emotionally attached to the characters, I cried, I cheered, I shouted - This is why I love Anime.