Ian - I came back on this route on 10 July. The A25 in France has a horrible surface in places. In fact I grounded the jockey wheel on this road and bent it, and it now needs replacement. I was returning from a 3000 mile trip and never grounded anywhere else!!
Also there were major road works on this road near Lille, with long delays - the signs were advising to detour via St Omer!!
On the way out we went via Gent and Brussels onto the A3 to Liege. This was excellent and we hardly noticed Brussels.
So I would advise going via Brussels!!
Keith