Masters of Sex
Loved the first season, but dropped out only three episodes into the second season. Never looked back.
Justified
Season five was bad enough we dropped out halfway through and didn't come back even though people say season six was a return to form.
Mildred Pierce
Literally debated watching each episode since none of them quite grabbed me and none of them seemed to point toward an actual story. Got through four out of five and just didn't care enough to finish it off.