Just finished Thr3e last night; couldn't make myself sleep until I finished the last few adrenaline-filled chapters :)
Really enjoyed the book. Although I'm not a horror-junky, I class this as thriller, rather than horror. ...
For me this was the first book in the series I read. In fact, my first Dekker book ever. I thoroughly engaged with it and loved it. I was initially confused by all the switching characters and such but once I had that down, I dove in.