I honestly really liked this scenario for flipping the usual script of pathfinder missions. Most of the time on an investigation you encounter the true villain right off the bat so the writer can do a 'gotcha' moment later on. It actually seemed a lot more like an episode of Criminal Minds, where the team has to track down a spree-killer before another person dies and they don't actually discover the psycho in the woods until the very last moment. While my players may have thought the necromancy stuff was cheesy, it did tie the serial killer stuff into the fantasy setting really well and explained all the enemies you faced. Said enemies certainly could have tactically been more of a threat though (and against a weaker or slower acting group, they might have been)
A main complaint was that the undead badgers at the end had no way of actually discovering the pathfinders easily when they started sneaking through the tunnels. Thus, they couldn't use their burrowing stuff to get the jump on them. The high tier digging enemies had tremorsense, which solves that problem. I also had a smaller issue with the restriction of the skeletons being unable to leave the bosses side. It would make a lot more sense for them to take advantage of their size in the tunnels instead of staying in the large room. Anyway, small complaints overall and I think most of that was solved at the high tier.
The only other issue was the whole background about the Linnorm King stuff. I'm guessing a lot of that is setup for a future scenario, but it really just felt forced into a really well crafted murder mystery scenario that had absolutely nothing to do with the stuff, other than as a foot note to explain why the authorities aren't looking into four bleaching deaths.
The DC's for the investigation skill checks also seemed really low, but I also had a few Perception & Diplomacy optimized players so maybe that was it more than anything else. I did like how the checks were formatted though.