I feel a bit weird giving all of the parameters a score of 10/10, but I have to say that I haven't seen such a great anime since Steins;gate.
(Fun fact- Both of them are about time travel)
So, This Anime is the kind of Anime you'll just stick to the chair and won't move until you've finished it all.
Story-
The story is well made, starts off GREAT, and all remains in mystery.
Satoru, as the synopsis said, is sent back to time, 18 years ago.
There, he's trying to change the future, and you're asking yourself while watching- "Will it succeed?", Will he fail?", What will happen if he does X instead of Y?".
It also doesn't feel too rushed, maybe in the middle you'll have about one episode that you could feel like they needed to fill something, but generally the anime's pace was good.
Art-
Nothing to say about it, it's colorful and beautiful.
Sound-
Hmm the soundtrack was nice, but didn't find anything special, besides the Opening song, which was GREAT in my opinion.
Character-
The characters in the anime developed well, and most of the "main characters" didn't stay "flat".
OVERALL+ENJOYMENT:
The mystery and excitment in this anime is great and tensing, you just won't stop watching until the very end.
10/10 RECOMMENDED TO THOSE WHO SEARCH FOR GREAT ANIME
