First, the candidate marks the return of John Locke, IMO... Come on, they give him so much character in this episode, he HAS to come back in some form... He'll have a very important part to play over the next few episodes, even if it IS only the FST... You gotta love what they've done with the character during the series :) Especially the bit outside the submarine where Jack says, "John Locke told me i had to stay" and then pushes him in the water! That's Epic!
Second, whilst it is upsetting to see Sayid die, it is cool at the same time... because now if you think about it, it all makes a lot of sense... This is why Jacob killed Nadia (indirectly), and Illana brought him back, and Jacob gave the message to Dogen... He knew that the Monster would end up putting them all in a stressful, every man for himself position, and he knew that Sayid was suicidal enough to give his life to save the others. He gave his life to save the candidates, mostly Jack!
Third, Jin and Sun... I'm not really understand what THEIR purpose was, but it was a good ending for them, if a sad one. They stayed with each other to the very end :)
Fourth, So, now that two (or three?) of the candidates are dead, does this mean that Locke can slaughter the others without the whole manipulation thing necessary ? Can he kill Jack Hurley and Sawyer without the need to drive them into a submarine with a bomb? Cause I wouldn't have thought the three remaining Candidates would fall for that kind of thing again, not after losing so many...
Fifth, Lapidus is alive. I know it doesn't look that likely, but they would have shown his death if he died. They wouldn't just have him say "Ah Dyam" as his last words... Personally, I think he'll be used to bring back Richard Miles and Ben... He'll float to a shore, and bump into the three of them, trying to blow up Ajira... Even though i do think ultimately, they'll be killed by the Monster...
Sixth, Sayid's last words, It's going to be YOU Jack... I think this is basically strong enough to confirm that he's the final candidate.
Let me know if you agree with any of my thoughts..