
Christina M. Kim teams up with Jordan Rosenberg to give us the last "pure" Claire-centric. I put "pure" in quotes because I still consider "What Kate Does" to be a shared Kate/Claire centric.
Anyway, in flashbacks we discover that Claire's contentious relationship with her mother was already years in the making when they suffered a violent car crash. Her mother soared out of the windshield and into the pavement, putting her in a coma that wouldn't break before Claire boarded Oceanic 815.
Then we get some bombshell news: Christian is Claire's father, making Claire and Jack half-siblings. I thought it was an interesting revelation but I couldn't put my finger on why. After all, Jack and Claire didn't interact all that much beyond Jack treating her post-abduction and tending to Aaron's fevers/rashes. Nevertheless I tucked it away in my mind and assumed it would play a huge role in the series at some point.
On the island, Claire's struck with an idea — get one of the tagged gulls and attach a rescue note to its leg. Her plans are repeatedly foiled by Desmond, who continues his routine of protecting Charlie from certain death. Charlie inexplicably shows no faith in her plan either, initially claiming he doesn't want her to get caught up in false hope.
This is where I think the episode runs into a structural snag. In flashbacks Christian suggests that Claire must discern between hope and guilt. On the island, Charlie's urges her to recognize hope versus false hope. It feels like a "close but not quite" on the attempted parallel.
Anyway, the "A" Team reaches the sonic fence outside the barracks, the first time the pylons are seen in the series. Mikhail is pushed through the fence and left for dead, then one-by-one the team makes its way to the barracks. Tada! They see Jack playing football with the Others and that's our natural cliffhanger for the next episode.

Emilie de Ravin must have breathed a deep sigh of relief upon reading the script; finally she'd have a few scenes without a baby as the focal point. She'd also get to try a new personna on for size, this one known as "Goth Claire." I have to admit that every now and then I forget I'm watching sweet Maternity Claire in some of the flashbacks.
Emilie's performances on LOST are not Emmy material but she certainly holds her own, and in Par Avion she does have a number of impressive scenes. Her best moment is undoubtedly her visit with her mother in 2004, starting off with idle chit-chat but eventually breaking down into tear-filled apologies. It may just be her best showcase of acting on the series.
She got some major help from John Terry (Christian), who automatically brings a certain heft and credibility to any scene he's in.
I wasn't impressed with Julian Barnes (Dr. Woodruff) or Gabrielle Fitzpatrick (Lindsey), both of their performances a bit stodgy for my tastes.

Par Avion was truly a character study, which is my euphemism for suggesting there were almost no effects or visuals that really stood out. Mikhail's foaming-mouth "death" scene was curiously average for LOST. Even the crash scene in the beginning was shot post-crash with almost everything stationary/static.
The best I can do is assume the gull fly-aways were partially/completely CGI, in which case I applaud the realistic implementations.
In terms of directing most of the episode was standard but there was one shot that seemed to be pure luck. When Desmond reaches for a gull a wave crashes against the rocks, thoroughly soaking him and flinging water toward the camera. I love little visual treats like that, intentional or not.

Par Avion holds up pretty well for me in the longevity category but for all the wrong and superficial reasons. What can I say, I have a hopeless crush on Claire (all versions of her) and it's fun to revisit her goth stage. I also like to see rare combinations of character duos, in this case Christian and Claire.
Significance of the story is another matter entirely. I expected the Jack/Claire sibling arc to be much more influential at some point in the series. In fact at one point I was convinced that it'd be instrumental in breaking Claire out of her "infection" in Season 6. I'm fine with them not going that route but I do find it curious that it was mostly relegated to an "FYI" by the time all was said and done.
Sadly, Claire's plan with the gulls ended up bearing no fruit at all.

I'd say two moments carried a serious emotional wallop:
1. Claire breaking down crying at her mother's side. Any time there's an emotional moment between parent and child it usually gets to me. It always reminds me that it's important to settle family disputes sooner rather than later, for the day may come where you no longer have that chance.
2. The mini-montage where Charlie reads Claire's rescue note. You imagine the Giacchino score, I'll post the highlights:
"To whom it may concern,
We are survivors of Oceanic Flight 815. We have survived on this island for 80 days . . . We've been waiting here, all this time, waiting for rescue that has not come. We do not know where we are; we only know you have not found us. We've done our best to live on this island. Some of us have come to accept that we may never leave it. Not all of us have survived since the crash, but there is new life too, and with it there is hope. We are alive. Please don't give up on us."