Huh. Seems to be two to three trains of thought here:
1. Endings that weren't necessarily bad, but were depressing.
2. Endings that were done terribly, but to stories that needed some kind of ending.
3. (Some overlap with 2) Endings that kind took away the mystery to a story in some way and just shouldn't have been included / explained too much.
I guess Sopranos would fall into a 4th group, the opposite of 3, endings that didn't explain enough.