The episode did a lot for Lost. It created a framework for the show, using Jacob as bookends to the beginning and present, and finally proving that Locke has been right all along; they were all brought there for a reason. Whoever or whatever Jacob is, his motivations still remain hidden but his actions have proven that nothing has been coincidence in the show. Everyone was visited by Jacob and eventually brought to the island, but for an unknown purpose.
In that regard, The Incident contained one of the biggest answers we've received yet. But there were others; Locke's dead, Faraday's dead, Sayid will probably die as will Juliet, and Jack blew up a hydrogen bomb. Man, that's a lot. Both parts of the episode were jam packed with action and movement as Jack made his crusade to blow up the Swan Station to reset time.
The pacing and build of the episode were pitch perfect and just like the previous season finale, it featured a great Jack vs confrontation. This time with Sawyer, the conversation between the two titans of the show built in tension until the only way to break it was to punch each other.
The thing that I think is so great about this episode was the fact that we heard about the "incident" back in season 2. Never did we ever think that we would actually get to experience it! That is the great thing about Lost. Expect the unexpected, cliche as it is to say. Plus, ending on the biggest cliff hanger, this episode has been making me think since it aired. This episode alone is enough to get you pumped for season 6, so just imagine those of us who have the rest of the series to help us get excited.