Huge LOST fan here too. I thought it was a great opening and a good balance between answering some existing questions and kickstarting some new ones, especially how the two realities merge at some point.
The story has so many facets it's amazing, and the 'world' is so deep that it compares to some of the world-building Tolkein and Robert Jordan have done, even though it's set in a "real world" context (sort of). I still believe that at its core the 'big' personal story is a father-son one between Jack and Christian (and sometime Locke?). In many ways they've been circling around each other without interaction (especially since Christian's dead!), but his father still plays an overwhelming role in Jack's life even without direct contact.
Seeing the old (dead) characters has been great as well. I thought the Sun/Jin scene in the airport was terrific -- a great playback to the first season and demonstrating the huge changes that have occurred in their relationship. If things were 'set back to normal,' their renewed love story (and child) would be gone. Same with so many others, but that's one big example.
And as always, there's usually at least one jarring thing out of place. Started with the monster. The polar bear. The hatch. The Black Rock. The four-toed statue. And on and on. And for this season? Desmond!? Why the heck is he on the plane if things were 'reset' in the alternate timeline?