I'm Lost

I've watched Lost occasionally since the show premiered, but only since the recap show a few weeks ago do I feel like I know a little bit of what's going on. I watched the entire episode last week and was truly shocked by the ending. I missed the first half hour of tonight's episode, so I really don't know what happened. It also seemed like nothing too important occurred in the second half of the episode, but I could be completely wrong. Can anyone fill me in on what I missed and if what I did see was crucial to the plot? Thanks.