There's almost no point talking about javascript on HN with the amount of anti JS & anti framework rhetoric that happens here
I would give it 5 marks out of 10. It’s decent but not a bastion of good design.
Gov UK design system is poorly usable. From color use to disorganized, scattered layout; it’s put together with haste and not much thought.
What it’s good at is looking sexy and minimal which captivates a lot of people.