I'm very much with Flannen on the issue of Joss Whedon. Obviously, I love most aspects of his creative psyche or I wouldn't be here. That said, his work ethic and general personality don't fare well with me all that smoothly.
Plot aspects aside, (and I know this is a common reply in this thread but it needs to be said because it's true), what he did to Charisma Carpenter (not even Cordelia, the actress that plays her) was absolutely atrocious, and would cause me to never work with the man again. Cordelia Chase was a character with, arguably, one of the best and most developed character growth. While she had success on Angel, Joss basically ripped her away from Buffy and placed her in a whole different show, which Charisma was wary of, as stated in interviews. When he impregnated the character he also assassinated her, and she didn't deserve that.
Perhaps Charisma should have informed the staff that she was pregnant, Joss definitely overreacted and honestly had no place to. It was Charisma's choice, not Joss's, and for her to be basically reprimanded for it was both immature and detracted from his character. Even recently she issued her thoguhts at a panel convention, and it's available on Youtube for anyone interested on what she has to say.
Other things that ruined him for me were his plot over character mentality. If he needed ratings, killing off a character was no problem for him. And his mask of saying that the character needed to grow, and that's why he/she needed to go, quickly wore off after Joyce's death.