The essential "Lost" - which episodes?

Ok, I’m thinking about catching up on some Lost, all the way back to Season 1…which are “essential” episodes? I don’t want to get tied up with all the “fluff” in the mid-seasons. Do they have “summary” episodes that tie everything together after the mid-season breaks?

SORRY, MODS - missed the other thread about Lost on Hulu, which is essentially the same question I had.