"Ariel" is probably the most series mythology-focused episode since "Bushwhacked", this time turning the camera on Simon, River, and Jane, that story being built into a heist episode. There is a significant amount of character development in this episode and it's quite satisfying in that regard. The actual heist story itself, on the other hand, was rather mundane and the characters not featured largely relegated to simply pushing the plot, leaving the episode not quite as strong as the better episodes.
The story begins with the crew visiting Alliance stronghold named Ariel for Inara's annual mandatory medical check up when River suddenly lacerates Jayne with a knife. Jayne's upset and Mal tells Simon to get a lock on River, so Simon then comes up with a plan to help River and make the crew some money at the same time: steal medical supplies from an Alliance hospital. Simon clues the team in on what to take and where to take it from, and while the team is stealing supplies, Simon will be taking River to get her brain scanned. With Simon's knowledge of hospitals prepping the team, what could go wrong?
I like that the episode actually really moves the story between the characters forward for the first time in a while, aside from the flashes of romantic entanglements between Inara and Mal in "Shindig" and "Our Mrs. Reynolds". The tension between Jayne and the Tams planted in the pilot comes to a boil here revealing a bit more about Jayne as well as the Tams as well, although what we learn of Jayne is more interesting. Still, we see a return of the blue-gloved men this episode as well, upping the mystery of what happened to River and who she is to the Alliance.
That said, the rest of the clue, while still getting plenty of screen time due to the need to execute the heist, don't really have much of a story beside the mechanical completion of the heist, except for a slight moment of revelation from Mal in how he regards his crew, including Simon and River. But because there's little real investment in the heist or use of the heist to drive and develop the other characters, their scenes just fall kind of flat. However, the episode comes together towards the end during the chase and rescue scenes and the final moments between Mal and Jayne plus the Tam Siblings.
The setup and prep for the heist was good, as was the aftermath, but I think the episode falls apart a little in the middle. If there were bigger stakes or investments in the heist for Mal and Zoe specifically, but the rest of the crew as a whole, I think it might have been more thrilling, but even when things were going wrong, I never really felt any sense of tension that they were really going to go wrong nor what would happen if they went wrong. Part of that I think is a problem with the writing and the other part with the direction.
But despite the flagging middle, because it wrapped up well enough, I still found "Ariel" to be a decent episode and it certainly makes me wish that more episodes could really work to advance the story more. 7/10