The Maginot Line was criticised for not continuing all the way to the Channel coast, but that's a harsh judgement.
Military thinking at the time was "if the Germans try to outflank the Line by going through Holland and Belgium, they'll never do it because most of the French Army (millions of men) will be densely concentrated along the short length of frontage between the Line and the coast, and the Germans will never get through".
That would have been true except for one thing- the new Blitzkrieg concept whereby the main spearhead was directed at a very narrow sector in overwhelming strength, guaranteed to pierce any 1940 defence.
Later of course, the Russians showed how to stop the Blitzkrieg by placing masses of tanks and AT-guns in the path of the spearpoint.