I think there are three big problems facing the show right now. I'm still going to watch every episode, of course, but they need to resolve these problems fast or the final season just won't be that great:
First, there's no mission. The first few seasons, this was obvious: get off the island. But now, some of them have been off, and nobody (Sawyer excepted) really seems to give that much of a shit whether they stay or go. In fact, none of them really seem to care about anything understandable, beyond survival or finding someone else. Without that driving force, the show is dramatically inert.
Second, there's no mystery. They've revealed too much, and at this point, the only thing we know we don't know is who exactly Locke is, and what his plan is. But pretty much everything else of consequence has either been explained or dropped (what happened to Charles Widmore?) Previously, everything we cared about knowing was unknown - what's the deal with the island, who are the Others, why is there a polar bear, what's the smoke monster, etc. Now, there are a few new characters whose identities or motives are mysterious, and that's about it. Even if there are many new surprises awaiting us, we don't KNOW that we don't know them.
Third, there are no stakes. Too many people have died and come back to life for the audience to really believe anyone dies on this show. The whole parallel universe thing means that even if something truly awful happens on the island, the characters we love will still basically be ok. And there just seem to be so many deus ex machinae that we can't take any bad thing at face value.