The story revolves around the fateful decision of a mother to give up care of her daughter to the grandmother, and inevitable repercussions which follow, but the key issue of the play as I see it is control. Mothers try to exert control over their own daughters while, being daughters themselves, they strive to break free from their own mothers' attempts to control them.
This is definitely modern theatre; the story is presented in a staccato of short scenes, which jump from one set of characters to another. Unfortunately, the many scene changes take a little too long and break the atmosphere, while the looped set change sound effects quickly begin to grate. The sideline plot, following a group of little girls, also becomes vexing; the link to the main story is dubious and the children always seemed to shout and fidget, as if they'd had far too many sherbet sweeties.
Though the portrayal of children was suspect, the way the older generations were represented was often spot-on. The frailty, resignation and regret attributed to the great-grandmother were beautifully done, and the bitterness of the grandmother was very convincing indeed. While the acting was sometimes clearly amateur (cups full of hot chocolate swung carelessly, a pain in the stomach instantly forgotten) I was still genuinely moved towards the end.
As with many things, the way in which you approach this play will determine how much you enjoy it. At £8.50 one should not expect the Royal Shakespeare Company, and if you go in with such expectations all you will be able to see are the holes. But if you come expecting simply to be entertained, to laugh a little, and to be moved a little, you will not be disappointed. My Mother Said I Never Should is a perfectly acceptable piece of amateur modern theatre.