Tir Sir Gâr, Carmarthenshire County Museum

The play is the thing, to quote one famous bereaved theatrical son, and in this new collaboration between Theatr Genedlaethol Cymru, artist Marc Rees and playwright Roger Williams, it is most definitely the thing.

A Welsh-language multi-media promenade production that takes as its themes the erosion of the traditions of agricultural communities, Tir Sir Gâr is a complex balancing act between fact and fiction, and between emotional, involving drama and cold introspective installation art. The balance is delicate, sometimes successful and sometimes not.

Granted, the story would not be enough on its own: the head of the table dies and the widow (Rhian Morgan) and offspring go through the mill, as it were, as they try to decide on the future of the dairy farm. Emmerdale recently ran the same story. But the strength here is in the superb acting that the cast bring to a very good script. Williams has the confidence to open up the drama so it is clear that although we are in Wales, and we are in the present, we are actually grappling with the plight of the working classes, yet again. The farm produce is driven to Crewe and back before the farmhands themselves can actually purchase it in the local supermarket (managed by daughter Luned). But this is the plight of rural communities the world over.

This broad universal brushstroke is the strength, also, of many of the installation videos that the audience are led to in between acts. They are solemn and reflective at their best. But too often, they bend over backwards to make artsy and obfuscating the very spit and gristle that this show is supposed to be celebrating. And what is that message? It appears to be that "times change" and "that is bad". It may be good material for drama – and so it proves here – but Tir Sir Gâr needs to go further to make its point with conviction.

Siôn Ifan stands out as Arwel, the son who has stayed at home, brimming with resentment and bottle-capped affection. Catherine Ayers is excellent as Luned, the daughter caught between the two worlds of her family’s traditions and the modern evils of corporate hegemony. But there is a problem here; when Luned’s mother scowls that the supermarket she manages is not a shop but a "shed", we are reminded of the Dutch barn where the promenade evening starts, and we are forced to wonder if modernism is not only entwined with inevitability, but if it’s also simply a colder repetition of patterns. These are the most profound questions that the play raises and then, too often, walks away from.

Tir Sir Gâr has flashes of theatre at its most moving, and suggests moments when the conversation might really take flight. But there are no remedies on offer. It is an ambitious attempt at tackling an old subject in a new way, muddied by the clutter on the peripheries of the main drama. The play is the thing - the rest could have been left behind.

• Tir Sir Gâr at Carmarthenshire County Museum until 27 January