There isn't really much of an "ending twist". The so-called "twist" at the end is only a twist insofar as it reveals the true nature of the alternate timeline present only in Season 6. Since it doesn't have any bearing on the first 5 seasons, I would say it is very much worth watching. I agree with HM03, though. The 6th season was my least favorite, but it doesn't invalidate the rest of the show. In general I think people overreacted to the ending. The show was still good even if we find out that Spoiler the flash sideways timeline, present only in Season 6, was really the afterlife.