Because You Left: Average. Sayid's fight was kick-ass (especially the playing-possum part) and time-travel hijinks are always fun, at least on
Lost (due to the writers showing some ability to think about time travel rather than just toss a lot of arbitrary shit our way), but the spectacle of Our Heroes being smacked around by time-fu wasn't very compelling or very original (tho it's a new element for
Lost) and frankly I was getting a little bored by all the bickering and tromping through the jungle.
And "solving" the dilemma of protagonists being helpless because of predestination by arbitrarily designating Desmond as magically special (I'd like a good explanation for that, tho I don't expect it) smacks of cheap writer manipulation and awkward retconning (since Desmond has already been established as capable of changing the timeline). I know they're trying to avoid the greater problem of total chaos breaking out if all the characters can change the timeline, but this kind of fishy writing reminds me uncomfortably of the patchwork time-travel rules of ENT, and that makes my tummy hurt.
Also, I still don't get the logic of the Oceanic Five lying "for the sake of the people on the Island." Widmore won't believe the lie, so why bother? If everyone tells the same crazy story, the worst that will happen is that the world will believe they suffered a mass hallucination due to trauma, they will be checked out medically, but since there will be no further evidence of insanity on their part, or evidence one way or the other about their story, they will be released to go about their merry lives, and they will have nothing to feel guilty about.
Poor Hurley was right and apparently the only one who was thinking clearly at the time. Then again, it was Jack's idea, wasn't it? And it's a wonder any of them would have been thinking clearly. I can buy this angle as a poorly conceived plan borne of panic and stress, that they were locked into even after they'd had a chance to reflect on it, but Jack really owes Hurley an apology.
The Lie: Excellent.
Much better, with a lot of great character moments. The powerful scene between Sun and Kate, Hurley's insistence on telling the truth and his mother believing him, Sawyer rescuing Juliet (the start of something...? says the obnoxious little shipper voice in my head

), Hurley threatening not to help Sayid in the future and then forgetting all about it. And funny/revealing stuff like the horrible decor of Casa Reyes, the "dead Pakistani on my couch" and Sayid briefly trying to murder Jack. And Hurley's inventive scheme to evade Ben's grasp, all great stuff.
But as always, it's meaningless to rate these episodes individually. Because You Left was also a nice set-up to The Lie, and if there were some draggy parts, it was in the service of a greater whole, and together they add up to a high Above-Average.
Season 1: The Crash
Season 2: The Hatch
Season 3: The Others
Season 4: The Rescue
Season 5: The Return
Season 6: The Really Really Really Really Large Turtle Under the Ground
My guess about the island? Not only is it jumping in time, but also in location as well (hint: the pendulum marking various locations on a large map)...
It would be easy for time travel to be causing the changes in location, either because the Earth is spinning, moving in orbit, the Universe is expanding or the Turtle is just getting restless...