The 42nd Amendment Act, enacted in 1976 during the Emergency period, is widely regarded as a 'mini-Constitution' or a comprehensive revision of the Indian Constitution due to the sheer volume and fundamental nature of the changes it introduced. It touched upon almost every part of the Constitution, significantly altering its structure, spirit, and balance of power.

One of the most significant changes was to the Preamble, where the words 'Socialist,' 'Secular,' and 'Integrity' were added. These additions fundamentally redefined the nature of the Indian Republic, reflecting a shift in the state's ideological orientation.

The Amendment also introduced Part IVA (Article 51A), incorporating Fundamental Duties for citizens for the first time. This was a significant philosophical shift, balancing the rights of citizens with their responsibilities towards the nation.

Several Directive Principles of State Policy (DPSPs) were added or amended, such as promoting equal justice and free legal aid (Article 39A), participation of workers in the management of industries (Article 43A), and protection and improvement of environment and safeguarding of forests and wildlife (Article 48A). The Act also gave precedence to DPSPs over Fundamental Rights in certain cases, a move that was later largely reversed.

In terms of parliamentary supremacy and judicial powers, the 42nd Amendment made drastic changes. It curtailed the power of judicial review of the High Courts and the Supreme Court, particularly regarding the validity of central laws and constitutional amendments. It also extended the term of the Lok Sabha and State Legislative Assemblies from five to six years, effectively prolonging the tenure of the government in power. Furthermore, it made the President bound by the advice of the Council of Ministers, limiting presidential discretion.

The Act also facilitated the creation of Administrative Tribunals (Part XIVA) to adjudicate disputes relating to service matters, thus reducing the burden on regular courts but also creating parallel judicial structures.

Other notable changes included provisions for the proclamation of Emergency, making it more difficult to challenge, and strengthening the central government's power over states by allowing it to deploy armed forces in states without their consent.

The cumulative effect of these extensive amendments was a significant centralization of power, a curtailment of judicial independence, and a redefinition of the relationship between the state and its citizens. Critics argued that it fundamentally altered the basic structure of the Constitution, moving towards a more authoritarian system. While some changes were seen as progressive (like environmental protection), the overall impact was so profound and widespread that it went beyond mere amendment, constituting a comprehensive 'revision' of the original constitutional document. Many of its controversial provisions were subsequently reversed or modified by the 44th Amendment Act of 1978, highlighting the extent of its departure from the original constitutional scheme.