I dislike cliffhangers at the end of a season, because too often the interesting series that I'm following gets cancelled and the entire series thus ends with an unresolved cliffhanger.
Cases in point: The science fiction series Odyssey 5 and Alphas and the drama/ comedy series Popular.
But if a cliffhanger is well done in a two parter episode or in the middle of a series I can enjoy them, because they keep me interested wanting to know how it turns out.
Never knowing/ not knowing for a long time how it turns out is why I dont like them at the end of a season.
Good mid-series cliffhangers especially are found in the Eccleston and Tennant series of Dr. Who. They really had me eagerly awaiting the next episode.