Two players. Two sides. One is light, one is dark.
- John Locke, pilot episode of Lost

If most fans and critics agreed that last week's episode of Lost was lackluster, what adjective would be used to describe "The Substitute?" Suspenseful? Incredible? Life-altering?

During an hour that featured John Locke in his sideways 2004 world, and the Man in Black (MIB) taking Locke's form on the island in 2007, we were treated to a dizzying number of answers and revelations that might make it difficult to sleep for days. Let's get right to the reveals, many of which created a slew of questions themselves. This is Lost, after all...

"Jacob had a thing for numbers." With those words, Fake Locke revealed an answer fans have been anxious for since season one: The castaways alive in 2007 have been assigned one of the digits that have plagued viewers' minds for years: 4, 8, 15, 16, 23, 42. Scratch that, actually. Fake Locke crossed out Real Locke's number-four. Awesome, creepy stuff.

Let there be... dark?!? However Lost ends and whatever you think of the answers we'll receive along the way, it's evident Carlton Cuse and Damon Lindelhof have known where this drama was going since day one. Astounding case in point: Fake Locke enters the cave that seemingly housed Jacob, removed a white rock from a scale and tossed it into the ocean. "Inside joke," he told Sawyer.

But it's not so inside to long-time viewers, who have noticed numerous references to light vs. dark since this iconic scene in the pilot episode:

[video url="http://www.tvfanatic.com/videos/backgammon-scene/" title="Backgammon Scene"] [/video]

Does dark = evil? This is the question on the forefront of my mind now. We're clearly meant to believe that Fake Locke has evil intentions (he's gonna kill everyone Sawyer cares about, right, Richard?)... but what if the opposite is true? We know he told Sawyer a partial truth about Jacob: his nemesis may not have been pulling the strings of every castaway throughout their lives, as MIB stated, but we know he interfered at crucial moments and took actions that led them to the island.

What if Jacob never gives young James Ford that pen? Does he finish his letter to the real Sawyer? Does he end up in Australia, murdering the wrong man, fueling his bitter rage and then wind up on Oceanic Flight 815?

Jacob may have had pure intentions, but an argument could be made that he messed with these people's free will - and that's clearly a significant issue on the island.

What are these rules? You remember Ben's shocked response when Widmore's mercenary killed Alex, right? He broke the rules. It's a statement that has bothered us ever since. There are rules on an island that jumps through time and heals the wounded?!?

Apparently so, and they seem to be based around the concept of free will. Jacob made it clear to Ben, seconds before he was murdered, that Ben had a choice. He told Hurley the same thing about getting on the Ajira flight to Guam. Now, a random jungle kid (and about that appearance: WTF?!?) shows up and tells Fake Locke he can't kill Sawyer.

Our best guess: for whatever reason, these castaways must be free to make their own decisions. However, both Jacob and MIB have taken extraordinary measures to influence these decisions. For what purpose?

Fake Locke's response to random jungle kid, meanwhile, stood out in an episode full of meaningful quotes: DON'T TELL ME WHAT I CAN'T DO!

Where have we heard that before? In his revised 2004 world, Locke may have had some problems, but his universe appeared to be on track. He was engaged to Helen, he had a good relationship with his father. Moreover, by the end of his arc, John had accepted his wheelchair-bound fate and even mocked himself for giving the walkabout folks his classic line, as quoted above by his quasi doppelganger.

What does all this mean? We can't say for sure. But for the first time, there seems to be a connection between the sideways worlds. The 2004 Locke has learned lessons the 2007 version struggled with for years. Did it take Locke dying for his consciousness to be transported to a different timeline? Why would the Man in Black suddenly show the kind of fear and anger (after falling down, remember) that dominated the man in whose body he now resides?

John Locke may be buried in the sand, but he's still alive in multiple ways on the island and in 2004.

Hurley also had great luck and Sawyer seemed mighty happy when we saw him in LAX, didn't he? Will the lives led and the lessons learned on the island somehow translate to a 2004 universe where these survivors are given a second chance - something Fake Locke told Richard was rare - they actually take advantage of?

We want to give readers plenty of time to share their opinions, theories and questions, so let's switch to bullet points:

• Why would Jacob be so interested in "candidates" to take over for him? Was he dying?
• More connections, aside from the great scene above, to past episodes: Locke has always been able to control Sawyer in ways others cannot. Think back to "The Brig" when Locke was about to manipulate Sawyer into killing his father.
• There was only one number (42) assigned to "Kwon." Does this mean either Jin or Sun will die?
• Where does Ilana fit into this? She gathered those ashes like there's a clear purpose for them. To ward off Fake Locke?
• How cool was the Smokey point-of-view shots to open the episode?
• How amazing is Terry O'Quinn?
• There was no number that corresponded to Kate.
• The most important development of the episode in our view: the island storyline is now clear and simple (for Lost, that is): Fake Locke wants to go home and he wants to recruit others to join him. There's a lot that remains ambiguous, but it was important to frame these events, and set the final season on a clear path toward... wherever it ends up taking us.
• Is the young kid in the jungle... Jacob?!? That's our working theory, as he had a clear message for MIB and even resembled the adult version of this character.

So, you tells us, readers: Did we just discover everything we ever wanted to know about the island?!? What blanks still need to get filled in? What did we miss in this review? Are you happy with these answers?

And has your heart stopped racing yet?

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.