Shadowfever easily could've been reduced to 400 pages IMO. The plot was dragging its ass through almost six hundred pages and only the last fourty or so did it become engaging. Before that the plot danced circles around what Mac was or wasn't. It became borish due to the length of the story. Everything is implied and very little is answered. When I'm lead on like that for more than four of the six hundred pages it tends to irritate me.
The MacKeltars. What happened to the fierce MacKeltars?! They were limp noodles in Shadowfever bickering with V'Lane, the Sidhe-seers and Barron and his crew on what to do and how to do it. Their importance, which was implied in the Highlander series, was next to zilch in the Fever series or Shadowfever. Big let down! The only MacKeltar whom was remotely interesting was Christian. But I guess he needs to be since he's going to play a part in Dani's story.
V'Lane and the Unseelie King, amazing characters, great background stories. Their story twist and turns kicked in a surprise factor I didn't expect by that time in the book.
Mac and Barrons, I can not say their story was romantic but they fit somehow. Really enjoyed how they interacted and brought some fire to the pages!
The plot conclusion was underwhelming in the first part but the second part made me sit up and pay attention. It contained a twist I really liked!
There is no true ending. Nothing is like roses and daisies at the final page but hopeful. A spin-off with Dani will be interesting!