As an Englishman, I can tell you the EU is a socialistic con.
The French will tell you that it's the best thing since sliced bread.
The muslims will tell you: "thanks for the free money and housing infidel".
I have to disagree.
The main critisism of EU comes from the political left, who believe EU is a threat to laborers unions, to regulations in different work sectors.
They argue that EU has become an neo-liberal economic experiment, a capitalist experiment where the lowest bidder will win.
Some economical analysists have a slightly different perspective on labor unions, and actually sees them as a vital part in making capitalism function.
The argument for strong labor unions is that Europe will never be able to compete with low prices, since there will always be a country in the world where lower wages can be offered. So the only thing that Europe can compete with is high competence.
Meaning that if unions are allowed to keep up wages, ineffective companies will fold, and only the strong will survive.
This is how some economical analysists generally explains the idea of a strong union.
Of course, some economical thinkers opposes the idea of unions altogether.