I think the problem with Lost was that the writers got to going and never wanted to end it. After season 4 they should have been thinking of tying up the loose ends and giving closure. At the time, they claimed that the ridiculous ending was as they had envisioned it but later, they have gone on record as admitting that they had painted themselves in a corner and had no idea how to get out of it.
As for Battlestar Galectica, I saw that ending coming about a year early. The foreshadowing had basically tipped their hand and I was not surprised to find that they were not our descendants but instead our ancestors. I thought that it was brilliant. The human religion set the basis for the Greek and Roman beliefs while the Ceylon religion (and with the human converts including Baltar) was the basis for Judeo-Christianity.
Saying goodbye to some characters, I found the execution of Gaeta somewhat disturbing, Callie's murder was upsetting, while
I hated to see Boomer die (she had been a favorite, the fact she was killed by one of her duplicates, Athena made no difference)
I was never clear as to the faith of Kara (Starbuck). Was she an angel of sorts?
All in all I found the finale satisfying, unlike that ABC show that ran for six years about plane crash survivors...