This is a solid Primark. I was there on a Sunday right before closing. At about 10 minutes before…read morethe store was scheduled to close, they made two announcements, one in Dutch, one in English, that the dressing rooms were closing and the store would close within 10 minutes.
There are three levels. You enter on the ground floor (duh) and go down for men and up for accessories. Since the store seems pretty new, it is also pretty clean.
I didn't purchase anything this time but there was a decent Harry Potter collection and dedicated sections for pajamas, bags and underwear, as usual.
It is definitely a medium-sized Primark (I've seen both bigger and smaller, for example, the Amsterdam store is much bigger) and it is conveniently located centrally in Groningen.