I don't want to write a thesis here, but hopefully a bullet-pointed list will suffice:
* The EU is not only undemocratic in the sense that the powerful European Commission is unelected, but is in fact antidemocratic in the sense that one generally has to have lost a democratic election in one's own country to be appointed to it.
* The EU places an enormous regulatory drain on its member states, issuing a stifling number of pro-corporate, anti-free-market regulations every year
* Policies such as the Common Agricultural Policy, the Clinical Trials Directive, and the Port Services directive are extremely illiberal policies, introduced to satisfy special interests.
* The EU is in the process of exporting draconian, crushing German-style data protection law to the rest of the continent.
* The European Court of Justice is not only activist, but also highly incompetent, lacking the institutional jurisprudential experience of proper supreme courts, such as those found in the UK.
* The Common Market is not a free trade agreement, it is a customs union. Combined with the EU's inability to negotiate free trade agreements (held up by Italian tomato growers, French vintners, and just about every other special interest wanting protection), this means that export-focussed economies such as Germany's are hampered from engaging with faster-growing economies - and just about every other continent's economy is growing faster than Europe's.
As I said, I don't want to write a thesis here, but these are just a few of the many reasons why I believe that Germany - and almost every other country in Europe - would be better off making its own laws by a democratic process, trading and cooperating freely with its friends and allies, rather than being part of an antidemocratic, supranational bureaucracy.