Season 3 of The Killing not as good as first two seasons - and here's why

I am enjoying The Killing Season 3, though with some serious reservations. Strengths are to a degree the elements that carried me through the first 2 seasons, notably the fine performances of Enos and Kinnaman (?) as the lead detecties tracking down who killed Rosie Larsen - Enos especially strong in the role, tough, dedicated, unflappable, but vulnerable at the core. Kinnaman terrific as the young cop and who emulates street talking ghetto folks - in one of the more memorable lines, a teenager asks him: Anyone ever tell you you're white? Well, both are still at it and strong in Season 3, and Seattle (Vancouver actually but who's counting?) still drizzly and evocative, cops still working a really tough shift and piecing together the clues through hours of drudgery not sudden and improbable coincidence or confession. That's enough to keep me going. However: one thing that made seasons 1/2 so strong were the many interweaving plot lines that led to a kaleidoscope of suspects including every character but Enos herself. Also, the personal saga of Enos - her background as a foster kid, her tough first marriage, her protection of her son, and her doomed-to-failure engagement - all made a seemingly opaque character much more deep, and more human. That's all gone - season 3 in a way could be any pretty good police procedural. Also, the investigation is far more gruesome and bizarre - a serial killer who has killed many young street women over seemingly many years - I get that he might not be caught so easily - in fact I think something like that happened in the Northwest, but surely people would be aware of crimes of this magnitude and would not suddenly discover a dozen corpses floating in a pond near the airport. Everything is leading us to think that the killer will be a lowlife who frequents the street haunts - all of which tells me that probably won't be so. But the reason season 1/2 worked well as a plot is that we knew the killer had to be someone already introduced - whereas in season 3 new characters keep passing through - suspect of the week - not as effective as establishing a cast of characters and shifting the suspicion around over time.