Regret really? Nothing... but I do feel a bit cheated when some programs you've spent a lot of time dedicated to end up crappy, like House had a shitty ending, CSI got reeeeeal boring - two examples I can think of off the top of my head!!
Parks and Rec and Star Trek I kinda regret too but theyre the opposite problem for me, I'm SO ADDICTED TO THEM I can think of nothing else most of the time...