I liked the finale from the standpoint it provided an overall explanation of what happens to the characters. Not perfect by any means but for the most part, the explanation was ok.
I agree that it could have been better if the writers had covered more of the mysterious points during the past year and I think that was the intent when the final date was originally set. The problem that occurred to screw up those plans was the writers strike which stopped writing and production after the date had been set. The timeframe the producers set to wrap things up was shortened and, IMHO, certain elements of the island couldn't be covered to everyone's satisfaction.
Some items I would have like to have seen covered was the concept of the island's mysterious powers, what was Dharma really up to, where did the Others come from (besides Richard) and why were the Others allowed to come and go from the island but not the 'evil' brother? The one thing from the last episode that seemed out of place was the fact that Juliette and Penny were in the last gathering yet they weren't on the flight. Where was Mr. Eko, Michael, Walt, Nikki & Paulo and Ana Lucia from the flight? -- > Libby and Bernard were there from the tail section and Ana Lucia was even there as the crooked cop in a recent episode.