@Another Movie Addict: I believe the entire build up with the potential army was wasted when Spike ended up taking out all the ubervamps with the amulet.
Then there was Willow and Kennedy. I recently read a comment somewhere that fans were pretty pissed off that the writers moved Willow on to another relationship so soon after Tara's death.
Spike's spotlighting as a rapist turned victim and hero was also quite unpopular.