Although Mere Mortals was still a fraking good read, unlike Gods of Night and Lost Souls which I read in a day, I took over a week to read it and the Hernandez/Caeliar sections of the book, although having ultimatily, the most segnificant outcome to the storyline, it for me, just dragged. I even remember through one chapter hoping it was almost over but it had another twenty pages to go! So yes, for me Mere Mortals does suffer a small amount from being the middle child of the trilogy. But saying that, the plus points of the book far out weighed the negative points.
Mere Mortals took me a long time reading as well - but unlike you, I enjoyed the Hernandez/Caeliar plot the most... everything else just seemed to drag on endlessly, especially the Hirogen fight. *g*