The first episode displays how good this anime can be at times. Amazing sound design and good visuals, interesting power levels... But it falls in quality very quickly.
Not only the technical aspects are lacking most of the time, character development feels rushed and shallow. The harem dynamic of the main trio puts me off the story at times, not allowing me to take in the interesting world the story takes part in. Even the "returned" aspect of the MC is almost gone after a few flashbacks of dead comrades, badly executed for a mechanic that's mentioned in the title.
On the other hand, the setting is interesting and the world is close to credible. The pacing is good (except some episodes) and overall it's still enjoyable. If you allow yourself to overlook the forced and corny harem dynamic (or if you like it) it's not a bad watch at all.
It's not the worst of the year and certainly not a bad way to pass time, but I find it very overrated. It's okay to like mediocre anime, but it's healthy to also know when it is, in fact, mediocre.