I agree with the consensus that the audio quality made this story very difficult to follow, especially in any sort of background noise (I listened to it in the car), even if I really liked the narrator's voice itself.
Given that, I liked what I heard (and Helena Bell's stuff in general) enough to go back to the EP website and reread the text afterwards, and I'm really glad I did. This story was outstanding and had a lot of depth to it, even if it makes you work to get at it. The story is very existential at heart: the world is slowly dying off and running down as people wait for the aliens to arrive, and as they debate the aliens' purpose and how to make contact. When the aliens do arrive, I think the implication is that the aliens were already dead or dying, and that their arrival was a final desperate bid to make contact and be remembered after their end. There's quite a bit of tragedy in the fact that the humans are also on the fade, perhaps partially because of the chaos of the aliens coming to Earth in the first place.
I especially loved all the building imagery suggesting the aliens' fate, and the theme of the difficulty of two intelligences trying to communicate. For example, you've got Kathleen thinking about dying and her bones falling into the ocean to be washed until they're like sea glass for someone else to collect. This mirrors the aliens' bodies adrift in the "sea" of space, shattering on Earth to be collected but not entirely understood by someone else. Then there's Kathleen's relationship to her ship, something she cares for but ultimately is forced to abandon, and the parallel to the legendary sailor YZ at the very end of the story, who experienced a moment of connection with the sinking ferry before they both died together. And of course, there's the metaphor of Kathleen's faith, and the question of how people relate to the supernatural, how such communication would need a Rosetta stone before any communication were possible, or else the message would be lost. The first problem of communication between two intelligences of any sort is establishing that you exist to each other to begin with. The tragedy is that sometimes we never get the chance to move beyond this, because by the time we're aware of it, it's too late.
To pick on a better-known example, I might compare this story thematically to "Ender's Game", if that's helpful for anyone, although this story is much bleaker and more tragic in many ways.
I also really enjoyed Bounceswoosh's take on it. I hadn't thought about the glass/mirror connection when I read it, but you're right: what the people read into the aliens' motivations very much reflect each person's character, from those who want to kill the aliens before they arrive, to people like Agatha who pray to God to bless the aliens as another beautiful and irreplaceable piece of the universe.
Good stuff all around, and it's a shame the audio quality understandably made this one hard to follow.