
This was the first truly kickass episode of Season 6 that got my adrenaline pumping and thoughts churning about the possibilities. Tucker Gates is a big reason this episode slams.
In the flash-sideways (FS), Locke returns from his ill-fated attempt at a Walkabout. This time we learn the trip piggybacked on company-paid travel, thus Locke is fired and forced to rely on a temp agency (owned by Hurley and supervised by Rose) to find work. The good news is he's reunited with Helen and their wedding plans are underway.
Once again the FS gives us insight into Locke's psyche at some point in his life. By the time he was paralyzed by Anthony Cooper he'd already lost Helen, but the FS shows us that he never gave up hope with Helen. He felt immense despair, convinced that even if they did get back together she wouldn't be able to cope with his disability.
It's also interesting to note how Locke becomes a substitute teacher in the FS, which isn't just a clever play on words or parallel to the theme unfolding in the island storyline. Ben is once again a veteran of an established system and is willing to make Locke his protegé.
On the island, fake-Locke (FLocke) hunts down Sawyer at the DHARMA Barracks and officially kicks off the Smokey Recruitment Tour. This is absolutely consistent with what the "dark force" has been doing all series long — pouncing on people when they're mired in misery and despair. Sawyer's in such a deep state of grief he doesn't even flinch at seeing Locke (whom he thought was dead). He doesn't even blink an eye when he realizes Locke isn't Locke at all.
The big reveal comes a bit later when FLocke leads Sawyer to a distant cave with numbers and names scribbled on the walls. According to FLocke, Jacob "had a thing for numbers". That's great but it raises the question of why the "official" numbers were broadcast as far back as Danielle Rousseau's arrival. Assuming the numbers were always linked to their respective candidates, why would Jacob bother bringing anyone else BUT those people? Was it all just a foregone conclusion? Did anybody have any say in the matter?
A few bonus points to Melinda Hsu Taylor and Elizabeth Sarnoff for writing a Locke burial scene. It didn't do much justice to the Locke we loved but at least gave us a moment to say farewell. More bonus points for FS-Locke falling onto his lawn and being doused by the sprinklers. Anyone who doesn't catch the parallel there wasn't paying much attention in Season 1.

Terry O'Quinn had already established himself as a phenomenal actor but he ascends to new heights in Season 6. In the flash-sideways he's gentle, down on his luck, insecure about his disability. The next minute he's the embodiment of pure evil on the island, manipulating Sawyer with promises and half-truths.
There are so many quality moments in The Substitute for TOQ but I'll narrow it down to my favorite three: 1) his berating of Hurley in the parking lot, 2) his conversation with Rose at the temp agency, and 3) his cave tour with Sawyer.
Speaking of Sawyer, Josh Holloway was the perfect "recruit" for Flocke, not just in terms of the story structure but also the pure chemistry between the two characters. Their jungle-trek conversation in The Substitute was a stark contrast to the one they held in The Little Prince.
I should mention that Jorge Garcia was very good in his flash-sideways encounter with Locke. Bonus points to Katey Sagal (Helen), for I loved the Helen-Locke dynamic 'til the bitter end.
Deductions for Zuleikha Robinson (Ilana), who simply couldn't decide which accent she wanted to use. It's particularly noticeable in her scene with Ben at the statue. Not only does her accent change, she's bawling one moment and then sauntering up to Ben like a porn star the next.

Tucker Gates hadn't directed an episode since Season 3's "I Do", and I gotta tell ya it was so nice having him back. His style is all over The Substitute and that's one of the reasons the episode looks so freakin' good.
The on-island stuff is obviously killer, giving us a first-person perspective of the Smoke Monster as it weaves through the jungle and coils over the landscapes like a serpent. The rope-ladder descent to the caves is also brilliantly shot, even if it raises the question of how the hell they got OUT of the cave.
Also note some subtle visual clues in the FS, notably the design of the mug Locke's holding while he's in the bathtub. One angle shows one side of the mug as black, the other as white.
But the reason Tucker Gates is potentially my favorite director is because he frames scenes in unconventional ways, and he knows which scenes to "stretch" for maximum impact.
Example:
Notice how in the FS we get quick cuts of Locke getting out of bed? That makes sense because it's not compelling television to cover every second of it. But when Locke gets on the van lift, there's no quick cut. Why? Because it elevates the humor and eventual shock of what comes next. That's the kind of stuff a gifted director does.
My only real complaint in this category: the obvious green-screening at the mouth of the cave. The studio lighting was way too artificial and FLocke throwing the stone into the backdrop wasn't fooling anyone. I would've preferred they skipped that bit entirely.

I loved this episode the first time around without even knowing what the FS represented. As is the case with most S6 episodes it got even better once I DID know what it was. As mentioned above, this was the first S6 episode to really get the juices flowing so it's fun to relive that excitement.
As far as significance goes I'll defer to the Writing section where I question the number-candidate pairings. At first glance it seems like a big reveal, but in reality it only introduces one more dimension to that mystery. Mother wasn't kidding... answering one question will only lead to more questions.

Atmosphere was heavily tilted toward the island storyline and I'm okay with that. Whatever the FS lacked in atmosphere it compensated with emotional resonance. Locke coming clean with Helen is a scene that makes my heart sink every time, especially this bit after he explains the walkabout:
LOCKE: They wouldn't let me go. And I sat there yelling at them. Shouting at them that they couldn't tell me what I can't do. But they were right. I'm sick of imagining of what my life could be out of this chair, Helen. What it would be like to walk down the aisle with you because it's not gonna happen. So if you need me to see more doctors, have more consults, if you need me to get out of this chair, I don't blame you. But I don't want you to spend your life waiting for a miracle because there is no such thing.
HELEN: There are miracles, John. And the only thing I was ever waiting for was you.