To echo what's already been said, I enjoy both open/ambiguous endings as well as gut-wrenching endings that completely destroy me. As long as the ending is well written, I will enjoy and appreciate it.

What I cannot deal with is yes, shows being cancelled on a cliffhanger, or shows completely losing it halfway or towards the end as they drag on and on. Nowadays I try to avoid shows with too many seasons or movies with never-ending sequels. Though if I'm being honest, badly written endings can also be fun because of the immediate boom of fix-it fics.