The EU-US Privacy Shield reflects the requirements set out by the European Court of Justice in its ruling on 6 October 2015, which declared the old Safe Harbour framework invalid. The new arrangement will provide stronger obligations on companies in the U.S. to protect the personal data of Europeans and stronger monitoring and enforcement by the U.S. Department of Commerce and Federal Trade Commission (FTC), including through increased cooperation with European Data Protection Authorities. The new arrangement includes commitments by the U.S. that possibilities under U.S. law for public authorities to access personal data transferred under the new arrangement will be subject to clear conditions, limitations and oversight, preventing generalised access. Europeans will have the possibility to raise any enquiry or complaint in this context with a dedicated new Ombudsperson.
I'm assuming the new agreement is incredibly complex and full of intricate legalese, so we'll have to wait until the agreement is ever tested in courts or otherwise comes under scrutiny from independent experts before we can reach an conclusions about its effectiveness.