I have to say that I rather liked it! Can't tell you how happy I was to see Shannon and Sayid together again!
I got the idea that the flash-sideways might not be purgatory, but where the souls of those who went on prior 'waited' until everyone else was ready to move on to the afterlife. I also thought it was brilliant to end the series with Jack's eye closing, when it started with his opening.
I'm not overly confused about things, kinda wondered why Walt and Michael weren't there, but as I read someone (I think?) that they aren't dead yet. Or, the time that they spent on the Island with everyone wasn't as meaningful to them as it was to the others?
I'm so sad to see the series done though.