I came to this very late as missed it at the time, but I love Stefan Golaszewski's writing on Cowards and Mum so happy to find it.
It's a nice little show- reminiscent of a series of little plays, especially with the enclosed setting for series 1-3. The show is really carried by the two leads who put in great performances and have fantastic chemistry. Shelley & Dan is a nice arc as well, and overall it captures a certain time of life really nicely.
As some others have noted Laura's character arc from tone deaf and narcissistic to plain evil is a bit much and strains believability to breaking point, but more positives than negatives for me.
Outside of the two leads the characters are a bit cartoonish, but Steve and Becky stand and watch this madness unfold around them and you see some great moments from them especially. Enjoyable.