I think the biggest problem right now is how slow the plot is moving for a monthly manga. While the premise and start were good, I think the author just doesn't know how to keep the world expanding and pace of the plot moving at a reasonable pace. I feel like the ambitious timeline really works against the story. It's like the author knows what he wants to do but doesn't know how to do it.
Edit: Another thing that I just thought about is that I'm wondering if the author will factor in things like his previous world knowledge working against him. This could be a pretty big plot point that leads to character development. Especially since the demons were VERY different from what seems to be portrayed so far. His information slowly getting less relevant and less helpful also needs to be considered by the author but it almost seems like he's trying to stall and artificially lengthen the "established time frame " by cramming more events (and increasing chapter count).
@Winzent I'm not sure if there was a pacing problem. The WN (not LN which this is based off of) was only translated to around V2C6 or so; it only really only covered up to the assassination of the king. That was the most solid arc of the entire series and while the other arcs were okay, this demon arc seems forced and is so far very badly executed in my opinion.