Your answer to this will of course depend in part on your own political opinions, but I am happy to provide you with some ideas to help get you started evaluating the Reagan years.
Many people who view the Reagan years as negative point to the negative impacts of the War on Drugs and his reduction in government spending. The Reagan administration escalated the War on Drugs, which strongly criminalized drug use without effectively reducing it. This led to many problems the United States is still dealing with, like high rates of incarceration particularly among men of color. It also generated a stigma surrounding drug use that makes it difficult for drug users to reach out for help.
Many people also look down on Reagan because his neoliberal economic policies fueled a reduction in government spending and thus significantly decreased funding for critical programs like education, food stamps, and social security.
However, many people view Reagan as a good president and point to evidence like the economic growth that occurred under his leadership. He enforced huge tax cuts, and the unemployment rate declined under his economic policies. He also strengthened national defense by increasing the defense budget and funding military research, and he played a crucial role in ending the Cold War.