This episode has generated some debate. Following a classic episode is never easy: "The Other Woman", which followed the classic "The Constant", was the lowest rated episode of the season. It's also a bit of a throw back to previous seasons, with a heavy emphasis on character development rather than major reveals and action as the last episode did. While it may be labeled "filler", it does offer some explanations for how Jack got to his meltdown in "Through the Looking Glass".
Jack's appearances in Kate's and Hurley's flash forwards hinted at the stupor he wound up in in his first one. There had to be something to get Jack from slipping a little liquor in his orange juice to popping pain killers like they're M&Ms. Playing house with Kate, while it may have satisfied some shippers, went against what was supposed to happen and those things are trying to "course correct". The prescription is the first step towards his addiction and falling out between him and Kate.
Ultimately, Jack and Kate turn into versions of their parents: Jack's an alcoholic who is unreasonably jealous and Kate is drawn to that. We don't know much about Kate and her mother's relationship besides her mom not understanding Wayne was a bad guy, but its possible Kate was a stabilizing figure like Aaron is to Kate.
Like Hurley, Jack is getting visions of someone close to him, in Jack's case his ever mysterious father. This contributes to his falling apart in the future as it did for Hurley. The second time Jack sees his father, it's after he changes a battery for the smoke detector. With that, the obvious implication is that his father is the Smoke Monster. It's probably misleading and some other island force (Jacob?) calling the Oceanic Six back.
With that, what would the island do to draw back Sayid, Sun and Kate? For Sayid and Sun, Nadia and Jin respectively would be appropriate, even if Jin is still alive on the island. For Kate, that figure might be harder. Claire would make sense, tying into the "you're not supposed to raise him" threat Hurley relayed to Jack. Targeting Aaron will be the only way Kate would be willing to give up her domestic, stable life to go back.
Kate's favors for Sawyer are likely those helping Clementine and Cassidy. Kate & Cassidy had a brief friendship in "Left Behind", so perhaps that back story was meant to do more than fill a flashback quota. Sawyer's recently stepped up as at least a protector of several people, notably Claire, Aaron and Hurley. In addition, Cassidy must've heard of 815, seen Sawyer's name among the casualties and then seen an opportunity when Kate pops up with the Oceanic Six.
It's interesting that in the Oceanic Six mystery, Sawyer had to option to leave with them, but chose not. Sawyer this season has been nobler than expected, acting as a protector towards Claire and her baby. With Claire missing in the end of the episode, he may stay behind because she's still missing.
Sawyer staying behind appears to have gotten under Jack's skin. It's likely whatever Jack's actions that got him off the island were, they sounded right at the time, but time has worn that down and he's justifying his guilt away. In that anger, Jack also makes a statement that could be read as acknowledgment that he learned that Claire is his half-sister. With family involved, that must make that guilt even worse.
Rose questioning why Jack's fallen ill could be a turning point in his leadership. The other person to get seriously ill with no provocation is Ben and that was one of the pieces that lead to the end of The Others' control of the island. Jack assertion that they'll "be ready" when the freighter arrives lacks the confidence and inspiration his words against The Others had just over a week earlier on the island. What did Jack do to anger the powers on the island to make him sick? The clear answer would be contacting the freighter and allowing them to arrive. This ties into his flash forwards, as living with Kate and Aaron goes against Aaron being raised by Claire.
In another shipper moment, Juliet remarks that Jack isn't interested in her the way he is towards Kate. It does make sense, as she picked Sawyer last season and Jack was willing to be unhappy if that meant she could be happy. While the writing indicates that Jack and Kate will wind up together, Jack and Juliet made a more convincing couple.
Claire's fate is the cliffhanger that ends the episode. Since her house was attacked, some have theorized that they are pulling a "Sixth Sense" by having Claire be dead already. Miles' interest in Claire and her baby is the strongest hint of that, but it may be just a red herring. This seems unlikely as it has been done many times before and would be hard to earn a satisfying resolution to that.
A more interesting venue would be the things she saw. A cut scene from the previous episode was Claire having some vision just before the mercenaries blew up her house. In this episode she mentions not "seeing things" anymore, which gets the attention of Miles.
The imagery of Miles with the hood over his head is clearly a call back to Charlie, but why that is isn't clear yet. Are we to believe they'll be a couple or will he make some contact with Charlie?
After the ambush of the mercenaries, to see five come out and only one is limping is a major disappointment. If anything, Keamy should've been the last man standing. This could imply some more rules Ben and Widmore are following, where he only sent the Monster to wound the men, but that cheapens the original action of Ben, having lost his daughter, unleashing hell as his last route out of the situation. However, it's likely that they have some degree of understanding of it, which may explain why they didn't suffer a similar fate to Seth "Pilot" Norris or Eko.
The appearances of the graves effectively dashes any hopes of Rousseau surviving, but that moment offers some insight to how Miles' gift works. He hears the dialogue uttered by Rousseau and Karl in their last moments in a more personal and intense manner than the rest hear the whispers. It possibly offers solid evidence that he is genuine as he knows their names without having given them, but he might've heard about them during his captivity.
One thing worth asking is how Rousseau and Karl were buried. Keamy and his men, the people responsible for those actions, wouldn't take time to throw them even in their shallow grave. The likeliest of solutions is that Frank, one of the "innocent" people on the freighter, did it out of the decency in his heart. If this episode does anything for the freighties, it's have them dealing with the actions of their violent counterparts. This may be similar to Dharma itself, where the hippies suffered the same consequences that those who fought with the hostiles did.
Daniel and Charlotte are certainly feeling the ill will on the beach, as no one trusts them after their lie is revealed. Things will obviously get worse when Sawyer and Miles (maybe Claire) arrive and inform them that the mercenaries slaughtered at least six of their people. Going to the medical hatch earns some good will, albeit not as good as Juliet got from Sun last season.
Jin's threat to Charlotte recalls his days as an enforcer for Mr. Paik. However, the decent man who loves his wife and unborn child above all else is still there. He's putting them above all others to get them off the island. This selflessness, in contrast to Sun wanting to save herself above all else, may be the biggest reason behind Sun's guilt in her flash forward.
Overall, this episode does a good job bridging that forceful post-strike return and the end game. Every character gets a little development, which is welcome just before the season's climax. There's only one normal episode left before the three-part finale, which means things should be accelerating once again.