(This post contains minor Lost spoilers up to S06E03. They are probably very minor, I have gone out of my way to avoid major spoilers, but if you're really concerned I'd suggest not reading it.)
Okay, I just watched the latest three episodes. I should start by saying I actually didn't find Season 5 all that wonderful. It felt like a great deal of the drama that made the previous seasons so great was lost in the spastic narrative. The only moment that was really gripping was the revelation in the season finale which had tremendous consequences on previous events of the season, causing a delayed reaction to a particularly significant event that didn't have much impact at the time. Now that's great storytelling. (Trying to avoid spoilers but if you don't get it I can explain what I'm referring to)
The first three episodes of the sixth season gave me the impression that this time the drama is back in full force. And I am glad. That scene with everyone leaving the plane except Locke was especially poignant. I like the new additions to the cast, and it seems we finally have a good villain again (something S5 sorely lacked, but not the seasons preceding it)
The only complaint I have is that there were actually less OMGWTFBBQ moments than expected. I've heard others who have watched the season première say they had no idea what was going on, but so far, this season is far more straightforward than any part of S5. In a good and a bad way.
I've so far considered S4 the peak of the series, but S6 has potential to change that.