There's a lot of speculation regarding ABC's LOST. Many have doubted if it would ever go anywhere.
I believe this season pretty much proves all nay-sayers wrong.
I was really happy with this week's episode, 316.
For the past few season's LOST has given it's loyal followers a ton of information that has often left us with dumbfounded responses and confusion. Season 5's pretty much turned that around with time hopping through windows and character ties that are starting to really bind the story.
I'd give more information, but really, you just need to watch.
...or you can try to watch LOST: Untangled. Which, honestly is awfully produced to make you feel like you're retarded rather than a Guide to helping you understand.
If you want to take a quick route, try just buying Season 4
and watching some of the recap shows online.