It doesn't really ruin anything, everyone dies- and that's the point. It's not like they all die in a fiery explosion, the epilogue of the series is just a fast forward to the moment at the end of each characters life. As far as what the actual resolution, or moment that the show ends on, I don't know because I haven't seen it.
I had an interesting conversation about Lost and heard some new theories.
-Here's one I just came up with, not really a shocking twist, just a thought. the reason that Sun didn't travel back in time is because they needed someone in the "present" to connect them to it, like Daniel's Constant. If they all went back in time, then they wouldn't have anything to connect them, and thus no way to return to the "present". Since the present is a non-existant thing, and there is neither future nor past, just different points in time.
-Jacob, or rather the person that we have been shown to be Jacob is not actually the real Jacob, and the real Jacob is Richard Alpert.
-The crew of the Black Rock are the Oceanic flight 815 passengers. People keep coming to the Island and having a conflict with the natives, but it's the same people every time. A pretty likely scenario I'd say considering that it was them in 2004 for 815 and them again in 1977 with Dharma.
-The end of the series will have them leave the Island, only to find themselves in a situation that returns them there yet again. (a variation on the loop theory where instead of starting out at the beginning again (going back in time) things just keep on repeating forward into the future.)
- This next season will start off with them having successfully reversed the circumstances to prevent the Incident and the plane crash, and they will just go on about their normal lives. All of the other plots will be dropped and no further explanation for anything on the Island will be given. So everything that everyone has been speculating about for five years will be meaningless, which is what the producers had in mind all along. (worst ending ever!? Although it is lent some credibility in being the one that no one expected.)