Well, it is what the French were expecting and planned for. Now, the German advantages of initiative and speed would still come into play, and just because the Germans would be attacking into the teeth of the French forces wouldn't immediately erase all the problems the French military of 1940 labored under.
French doctrine of 1940 didn't buy into the concept of successive defensive lines, even though the terrain along the border would be ideal for it. Instead they saw one line, continually plugged and reforming as it was pushed. In the context of WW2, this is a weakness. That being the case, the French will still deploy one powerful line of troops on their planned defense line.
When the Germans attack, their advantages in skill, and the basic advantage of the attacker in picking his target will allow them to concentrate overwhelming firepower on the French earthworks.
The French will then commit reserves, both laterally from other forces on the line, and from their central reserve. We know, from the historical Battle of France that these reserves will be moved into locations dangerously close to the front, but will also move into position at a much slower pace than the Germans can respond. Historically the Germans broke through the French defenses and then almost dismissively overran the still deploying reserves immediately behind the front lines. A lot depends on on how fast the Germans can penetrate the main French defenses in their main attack sectors, but looking at the speed of French deployments vs the speed of the Germans penetrating French lines suggests the advantage lies with the Germans here. It's unlikely they'll catch the French reserves quite as flat footed, but it'll still be a more fluid battle before the French are fully ready where the Germans will have the advantage. This becomes even more so since the Germans will launch several spoiling attacks and try and get the French to send reserves to multiple locations besides their main attack sector(s).
If the Germans smash the reserves sent to plug the gaps the French will try and reform the line rather than aggressively counter attacking with large forces, which inevitably means the Germans will advance, moving the main fight beyond the Line. If the French had a more offensive doctrine, bypassed portions of the Line could present a real problem for the Germans, but since the forces there will be static they quickly lose importance to the continuing fight. The problem for the Germans here though is the French front is stronger, the German advance will be slower, and Gamelin will just have more troops to throw at them. Despite the basic flaws in their method of fighting, the French probably will be able to pull a new line together further west, and hold the Germans again. By now the elite German troops leading the assault will be exhausted, with losses, and things will just start to slow down more. The Germans actually only had a small number of elite panzer divisions, and there's only so much you can ask of even the best soldiers.
Eventually the whole thing will grind to a halt, with the Germans having expended an heroic effort to overrun Belgium and even get across the border into France itself, giving Gamelin's forces a real drubbing in the process, but ultimately unable to actually get the breakthrough they really need.