The reactions I remember people having so far to the villain arc weren't particularly great, maybe it got better while I was letting the series stew for a while so I could just sit down and roll through the arc all at once. But the negative reaction was probably because they just started doing something new with the main character that's going to probably delve into the entire point of the series, look at the history of the setting a lot of people were curious about, then bam "And now for something completely different."
I probably would've had a better impression of the arc myself if it had been its own thing instead of more or less an interruption to what was already going on. I'm all for villain protagonists if the story is good, it can be a fresh experience after thirty billion or more goody-two-shoes being shoved in your face back to back. I think Zettai Karen Children did a decent go of things with their TV anime focussed on the guy who was more or less the villain up to then. It's all considered canon even for the manga, but it was still a separate thing that isn't strictly necessary to even see to keep reading the manga.