This is a real tough cookie to crack. Episode 11-16 is the biggest rough patch, then 17-21 are meh, then 22 is the amazing and infamously unresolved finale. Obviously the best scenario is to watch the whole thing, as things do happen in those episodes and the finale expects you to have watched them. Several ongoing plotlines either come to an end, or get a cliffhanger. But, it’s also true they’re pretty hard to get through especially if one is rushing through them to finish by Sunday. Previous events aren’t to hard to guess going by context clues, and probably about 75% of those episodes are complete filler that don’t affect the finale at all. It’s also a situation where I think the episodes are only tough to get through the first time, because one has certain expectations for the series. I had a hard time getting through it my first time, but I’ve seen the series 3 or 4 times since then, and now I actually enjoy those episodes for the most part since I have my expectations set to soap opera cheese instead of Lynchian madness. In truth, it really is up to the person. There’s no right answer.
I will say anyone preparing for season 3 should definitely watch the finale and the movie “Fire Walk With Me”. Both seem integral, and Lynch has actually said FWWM is one of the most important parts for understanding where season 3 is going. It’s a prequel, which puts off some people who were hoping for resolution after the cancelation, but I love the movie. Also if you can track it down (I believe it’s only available in the blu ray box set of the series and movie) check out “The Missing Pieces”. The original cut of FWWM was more than four hours long, and was cut way down. For many many years fans were hoping to see these scenes released, but even the DVD was missing them. Finally, for that box set Lynch himself edited them into a sort of companion movie. While nothing life shattering happens; there’s tons of scenes that are funny, heartbreaking, and everywhere in between. We get to see characters who weren’t in the movie, who we never dreamed we’d get to see again. There’s even stuff that takes place immediately after season 2.
Finally, for only the person who must see everything before season 3, the book “The Secret History of Twin Peaks” was released last year. Written by Peaks Co-Creator Mark Frost, it gives a history of the town as well as some hints of what’s to come in season 3. This book has been pretty divisive among fans, as it retcons a whole bunch of details, some small some huge, from the original series. I enjoyed my time with it though.