
BEN: It was on this island that everything changed . . . because exile wasn't the worst of his fate. What was truly devastating to him was the loss of his power. He might just as well have been dead.
The above quote from the flash-sideways (FS) was referring to Napoleon on the island of Elba, but it could've just as well been about Ben Linus himself. The last line is also foreshadowing in more ways than one — the Ben Linus in that scene WAS dead, and the on-island storyline had Ben digging his own grave.
The FS storyline of Dr. Linus is one that was completely redeemed by the finale. The first time around everything just seemed too convenient. Ben was taking care of his father (brilliant use of the oxygen tanks by the way) and Alex Rousseau was his biggest fan. At one point she shows up at his doorstep and, upon learning that he'll tutor her for an upcoming test, says to him, "You're the best, Dr. Linus."
It was all just too sugary sweet with Alex's adoration and Ben's decision to sacrifice power for her future. A couple months later I realized what a fool I was. Once again the FS gives us unique insight into the psyche of a character overwhelmed with regret, one who eventually realized his insatiable hunger for power destroyed his own life.
This theme bleeds into the island storyline, where Ilana forces Ben to dig his own grave as retribution for killing Jacob. Fake Locke (FLocke) approaches him at that grave, removes his shackles with a flick of his wrist, and extends an invitation to join his team. This would lead to a powerful scene between Ben and Ilana, one that reduced them both to tears. It is at that moment Ilana uses one of the most powerful tools of human goodness — mercy.
Jack, Hurley, and Richard briefly visit the Black Rock, where Richard pleads with Jack to end his life. The "new" Jack doesn't believe any such thing can or will happen, and sure enough he's proven right when a lit stick of dynamite inexplicably fizzles out. Well look at that, Jack has tapped into his sense of purpose. Jacob's strategy at the lighthouse worked after all.
An awkward reunion of Jack and Ilana's teams would follow at the beach camp, followed by the big reveal: Widmore's team has arrived. As Miles said earlier in the episode, "Ut oh."

This was the first time we got to experience adult Ben in an off-island environment, and just as Terry O'Quinn had mastered the ability to play two different characters in the same episode, Emerson showed he was capable of doing the same thing. In the FS he's a humble man who chooses an altruistic act over guaranteed power; on the island it's the devastating effects of power which have reduced him to a broken man and an outcast.
His scene with Zuleikha Robinson, where he insists Locke is the "only one that'll have [him]", was truly heartbreaking and a wonderful performance all-around. His tutoring sessions with Alex were a real study in how terrific an actor Emerson really is; study his facial expressions and mannerisms as Alex reveals the icky news about Principal Reynolds.
Right after the episode first aired I would've said Tania Raymonde's acting was below average. And I'd be eating crow now. I can't help but think she was given some guidance to act overly sweet, because I don't believe she would've hammed it up that much on her own.
Bonus points to Matthew Fox for the dynamite scene in the Black Rock with Nestor Carbonell. I remember many LOST fans posting online that they "loved the new Jack" and I can see why. Jorge Garcia, on the other hand, strangely regressed a bit this episode and was noticeably poor in that same scene. "Dude, you're gonna blow up!" was the line that really irritated me.

This was the only episode directed by Mario Van Peebles and it's a pretty solid effort. The episode's extremely dialogue-heavy so it was the ideal candidate to put in the hands of a "rookie".
The FS scenes were all nicely framed as well as most of the island scenes, with the exception of certain parts of the "dynamite showdown" in the Black Rock. Going with a wide shot while Hurley's pleading with Jack made Garcia's lines seem even worse. I also have no doubt that Tucker Gates would've framed the showdown in a very intense way, perhaps by slowly circling around the table while the fuse continued to burn. Instead it was simply alternating close-ups of Jack and Richard.
Once again the highlight almost has to be the sequence between Ben and Ilana. If the directing isn't solid during that scene it has no emotional weight, so kudos to Peebles in that regard.

The first 95% of Dr. Linus is fun to revisit, even if it's not my favorite Ben-centric in the series. The last 5%, starting with the reunion of Jack and Ilana's team, is awkward at best and the cliffhanger with Widmore was anticlimactic to say the least.
Ilana's mercy for Ben was critical in terms of Ben's overall redemption, though Ben would mostly fade into the background until the last few episodes. The Jack/Richard dynamite was significant in firmly establishing Jack as a man of faith, and may have been all that was needed to keep Richard on his side throughout the upcoming war.

The FS storyline is very touching when you consider the entire Ben/Alex arc throughout the series. It was simultaneously bizarre yet uplifting to see them enjoying each other's company.
And of course, the most emotional on-island moment was between Ben and Ilana.
If only I could reconcile the final scene at the beach camp. It's very depressing to see characters like Ilana, Frank, and Ben standing at the camp, which to me is practically sacred ground. That moment was clearly meant to be emotional but I'm sorry to say it fell flat. If you want a truly emotional reunion scene check out Season 2's "Collision".