First off, the ending made me cry like a baby. The goddamn dog lies down next to him as he dies?! Jesus Christ I was bawling.
Second, I still feel that the sideways stories were a complete waste of precious screen-time in the final season. It feels like a cruel joke about the common theory back in the beginning that they were all dead. Still, the bit in the church with Christian was pretty poignant. It was just a waste of half a season.
Third, everything else I found pretty underwhelming. We didn't learn a single new thing. There wasn't a single plot twist in the real Island story. The Locke confrontation was brief and completely anti-climactic. I spent the whole season waiting to see them actually do something against the Monster... and the black smoke form doesn't even APPEAR in the finale?! I had visions of super-powered Jack laying a smackdown on the Monster. An angry black form swarms towards him but flows around him harmlessly because he's immune to it. It tries to grab him with an appendage, but then Jack rips it off and then beats him down with it! Then he uses his super breath to suck in the entire smoke cloud, freeze it, shoot it back out, and shatter it into a million pieces while Locke screams nnnnnnnnnnnooooooooooooooo!!! Well, SOMETHING like that, anyway!
So on the whole, LOST is probably my second favorite show of all time, but the final season definitely wasn't as good as S3-5. Like so many shows before it, the ending was a disappointment. Actually it reminds me strongly of the horribly disappointing DS9 finale. The great and mighty destiny of the Sisko... was to chuck a book into the fire. The great and mighty destiny of the Jack... was to stick a stone pillar in a whole. Inspiring stuff.