The tax system reform is a part of Slovakia’s comprehensive tax and levies reform. The reform should contribute to improving and making public finances more efficient. Its implementation into practice, however, is problematic due to attitudes and problems on the part of both the professional public and business entities. The aim of the paper is to help public authorities, and also tax policymakers and business entities to understand the perception of the tax system reform focusing on the most important and key factors of its sustainable effectiveness and performance in the context of its non-macroeconomic especially social, technological and process aspects. The analysis reveals the differences in perceptions of key factors from the viewpoint of the three studied groups. The paper is based on the information of the main actors of tax reform. In extensive empirical quantitative research (N = 1500), the data was obtained through the questionnaire survey carried out in four main districts of Slovakia. The data obtained during six months of 2018 using the questionnaire method were processed by basic statistical methods of descriptive statistics, followed by an analysis of major components and the factor analysis using more sophisticated multidimensional statistical tools. The factor analysis is crucial to the present paper as it has identified five significant indicators of the reform assessment and the functioning of the tax system after tax reform. Subsequently, a correspondence analysis has been applied to the item “electronization/computerization—great user comfort” to find out the differences in its perception by the respondents. The article thus provides a new scientific view on the evaluation of the reform of the financial administration’s management system in the Slovak Republic as well as its functioning in the context of its sustainable effectiveness and performance. The research results offer important and exciting implications and also motives for further investigation on the issue.