The plot has advanced, the only problem is that even though it's advancing we still don't know why any of this is happening.
After all this time, no one has bothered to ask "the Others" the two stupidly simple questions that should have been first on everyone's mind:
Who are you?
Why are you doing this?
I think I'd feel better about the show even if we weren't getting answers, if only I felt like the characters were even bothering to figure it out.
In the end, I think "Lost" will end up a show better suited for DVD than for weekly broadcast. Because then I can watch it all in a couple of months instead of feel like it's dragging on for yeeeeaaaaaarrrrrssss.