I've been marathoning all of Season 1, 2, Fire Walk With Me+Missing Pieces, and Season 3 this weekend with some friends.
WOW there was more foreshadowing in Season 2 than I ever realized. This is my first time watching the whole thing together, and there's a lot of things towards the end of Season 2 which I never noticed before. Small things like how Mr. C's speech patterns are already present in Cooper in the Season 2 finale, clues about where the purple ocean place is, about the illness in Season 3, etc.
Very interesting, some of this stuff I figure may already be well known but being my first "complete series" rewatch with Season 3 included, it's quite a ride.