I haven’t read the original material, so I cannot say anything about how well/bad adapted it is, but I have a few things to say about this anime. You have probably already read the summary; this anime is supposed to be a symmetrical Isekaï with two characters from different worlds switching places. One world is modern Japan, the other one is common magic-based fantasy universe. Let’s say most of this anime revolves around the concept of TRUST, FRIENDSHIP and BETRAYAL. How can you trust someone? What does it mean? After being betrayed again and again by the ones you trusted most, would you be able to havefaith in someone again? These are the questions you will continuously hear in this anime.

Despite having a quite original and very promising double-Isekaï structure, making people expecting the plot to take place equally in the two worlds with two MC, the show is mainly centered in what happens in the magic-based fantasy world, with only very few stuff actually taking place in the “real world”, and that is too bad because this anime could have been so much better…
I have read a few other reviews, and I understand that this is precisely what many reviewers, having read the manga, give it grief for ; some elements taking place in the “real world” have been set apart to prioritize what was supposed to be the main plot.

12 episodes for this anime is too short, it could have deserved a 24 episodes season. (Well probably a second season was originally planned, but they unfortunately did not proceed with it.)

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OK and now you ask: “cmon you have rated it 8/10 but so far you only have regrets/criticism for this anime, so is it really worth-watching?” DEFINITELY YES, this anime has very few members rating it, and most of them are probably manga readers disappointed by the adaptation, resulting in global 6.5 rating which is not really fair in my opinion.

Art is good, so is animation. Fight scenes are quite rewarding and the rhythm is fine. The character development is fair for the MC and his “rivals” Kannagi and Kadowaki. Overall, this is good anime, far better than most 2018/19’s Isekaï and definitely deserves above 7 global rating. I would personally rate it 7.5, so it will be 8 to increase the global.