For Castle was a bad idea per se. But when the fan reaction can safely be compared to that of the ending of Stephen King’s The Dark Tower, or the final season of Lost, there had better be an amazing emotional payoff on the back end. The fandom is not impressed.
PS: I will say the conceit that both the NYPD and FBI failed to notice one of their officers was married when she claimed she was single was also highly dubious.
Great show. Not its finest moment.