I guess the writer hoped that giving the series such a downbeat ending might increase its chances of being renewed, if enough viewers want to see if things can get better? Kind of like a cliffhanger, but depressing rather than suspenseful.
Nicola Coughlan as Maggie and Lydia West as Eddie give strong performances, but the series seems more like sketch comedy with recurring characters rather than a coherent story. It might work better with a different narrative structure.
What was the audience meant to take away from this? That mental illness sucks? That chronic mental illness can mess with your friendships and prevent you from working? It succeeded in conveying that, and more -- even your best friend can be clueless about what you're going through, and good intentions aren't always enough.
Maybe watching this is useful for people who don't have experience of mental illness, whether their own or a friend or family member's.
But for me, it was just disheartening, particularly ending at that point in Maggie's story.