fundamentally i do think a big part of the reason spike is such a more interesting character than his many bargain bin imitators that have cropped up over the years is because the writers simply could not agree on who he was or what the fans should think of him. spike would not be nearly as good a character if it weren't for david fury's disdain for him or joss whedon's resentment of him or jane espenson's love for him etc. none of those individual writers could write spike but together with the other buffyverse writers they managed to create a very compelling, if admittedly sometimes confusingly written, character. many bargain bin spikes otoh are written by writing teams who all uncritically love them and want the fans to love them too and that is simply not how a proper spike should be written...it's just not!