Thatcher was not only a very good Prime minister, she was the right Prime Minister for her time and place. Britain had much post war success with very high tax rates and too strong unions, and she was very effective in lessening both and bolstering the economy, while also standing strong against Communism.
Thatcher's time in office was a mixed bag. There was a victorious war with Argentina over the Falkland Islands. However, there was also a push hard against labor rights and working families. There were rampant strikes and IRA terrorist attacks. In the end, her own party booted her out of office.