The European Union has been far more effective than the Maginot Line. That was one of the first mistakes France made that lead to WWII: being too harsh to Germany at the end of WWI, so that the German people were ripe for radicalization. The French should never have needed to defend themselves at all. Diplomatically, it's terrible. Highly provocative, loud in announcing distrust of a neighbor, and it looks weak next to a robust military.
But since the French couldn't bring themselves to make a lasting peace with Germany then, they had to think of defense. The Line is still a bad idea. When Germany reoccupied the Ruhr, all France had to do was rattle some sabers and they would have pulled right out. Instead they cowered behind a wall. When the war at last broke out, suppose the French had figured out that the Ardennes Forest was passable and had to be covered, either by the Line or the army. The Germans in turn would know this, and could get past the Line in many other ways-- paratroops, or another front the Line does not guard like maybe Switzerland or even Spain, or possibly a surprise amphibious assault via u-boat. They could also assault the Line. It can't dodge artillery. Punch through at a few points, and ignore the rest.