In honor of tonight's season 5 premiere, pick the best and worst episodes of the series so far. I'll start.
I'll start with the five worst, because LOST only has a handful of really awful episodes.
Stranger in a Strange Land: Can there be any doubt that this belongs at the top of the list? I was in denial about my favorite network show's decline at the time, so I defended it, but this was one of the worst episodes of TV ever shot. An uninteresting flashback - Jack the Ugly American's Thai Adventure - devoted to solving a mystery that absolutely no one cared about. Meanwhile, we're treated to lots of boring Kate & Sawyer crap and one of the lamest contrivances in the series when Sawyer lets Karl, who would've been very helpful back at the camp, run away. The writers introduce a crappy new Other character who seemed like she would become important but was ultimately dispatched off-screen in the Season 3 finale. There are one or two nice scenes with Jack and Juliet, but they can't redeem this turd of an episode.
Whatever the Case May Be: There a couple of forgettable episodes in the otherwise excellent season 1, but this and another are the only true stinkers of the bunch. It may be the worst Kate episode, which is saying something. In this episode, Kate drags everyone around her, both in her flashback and on the Island, through all kinds of misery so that she can get a fucking plastic plane back. Also, the titular Case is an actual case, which makes me hate the episode even more.
Fire + Water: Charlie in a diaper. There's a lot of bad stuff in that episode, but I'll let that statement speak for itself.
S.O.S.: Poor Bernard and Rose. They are good supporting characters, and they've had a lot of memorable scenes with the main characters. I really liked Bernard in all of his season 4 appearances. Unfortunately, they're not strong enough to be anything other than good supporting characters short scenes, so it's no surprise that this episode was probably the perfect example of what a "meh" episode of LOST looks like. It doesn't reach the depths of awfulness that Strangers in a Strange Land did, but the flashbacks are forgettable and uninteresting, the goings-on on the Island are insignificant, and it just feels like the writers are treading water until the season finale.
Born to Run: Shocking! Another crappy Kate episode. A lot of filler tended to emerge right before the season finales during the first few seasons. More uninteresting Kate backstory, the return of the plastic plane (because clearly that needed to be revisited) and an asinine plot about Sun poisoning Michael that shamelessly rehashes the raft-burning mystery from only five episodes prior.
Now the best episodes, which is a bit harder:
The Constant: It's a testament to the writing staff that this episode was basically carried by characters that weren't even around when the show was originally conceived. Probably the episode that really sold me on Faraday. Maybe the perfect LOST episode - it further deepens the mythology of the show, it pulls off time travel so well that it makes the HEROES writers look like clumsy children, and it has some of the series' most romantic, human moments. It was easy to follow, but in less competent hands would have been an absolute mess. Certainly my favorite episode so far.
Pilot, pts. 1 & 2: Still one of the best network TV pilots ever - maybe the best. It has great action, the emergence of many of the show's longest-running mysteries and does a good job introducing the characters. You don't need me to sell you on the why the Pilot was great - that's why you're still watching the show.
Walkabout: Sadly, the flashbacks reached their peak pretty early on with this episode. That's not to say there weren't any good flashbacks that followed this episode - there were - but none quite matched the gut punch of the revelation of Locke's condition and what that meant for the true nature of the Island. This was also our first exposure to the Survivorman version of Locke, which became less the definitive version of the character as the seasons went on.
Through the Looking Glass: The closest the show has gotten to matching the epic scope of the Pilot, this episode closes the chapter on the first half of the series, providing the Others with the comeuppance they so richly deserved and allowing the redeemed Charlie to go out on a high note. There is a LOT going on in this episode, and everything works. Of course, what really elevates this episode is the final five minutes and the revelation of the flashforward, which provided both a shocking moment for the season to end on as well as expertly setting up the last three seasons. Season 3 was not the best season, but it had the best finale.
The Shape of Things to Come: It was tough choosing a fifth - there are at least three other episodes that could easily be here - but this is a personal favorite. It's even better after you've seen the season 4 finale. Not as many revelations as the first Ben episode had - just a showcase for Michael Emerson and Ben the character. Always five steps ahead of the audience, Ben has contingency plans for contingency plans, and this episode shows it.