I don't mind that the characters are boring and generic, but ultimately there just isn't anything interesting about the show. There's no power progression like in most isekai. He just gets powers mainly offscreen. You just get to see him use the powers the writers say he has. The MC doesn't have a goal for the audience to relate to. The characters aren't dynamic enough to make it a slice of life.
The ultimate problem with this show is that they mix the first and third person perspective. Melfina is actually the words of the writer being communicated directly to the audience, and thus you just have to trust her on whatever she says. There's nothing to look forward because the writer tells you, and the MC everything out of the box, completely removing any suspense mystery or intrigue.
You can take a generic helpful character like kirito, and have him do the exact same things, and just improve the dialogue of the show enough to have a compelling story. That's what SAO abridged did and they created a compelling and interesting story just by editing the dialogue to add personality into the things characters say, but the screenwriters of some big anime studio can't do that?
tl;dr the writing is dogshit, the dialogue is boring and lifeless, and the writer didn't see that having an omniscient character directly server the MC would prevent him from ever being challenged in any way
