On one hand, Kissinger was undoubtedly effective at achieving America's foreign policy goals and was undoubtedly one of the most influential Secretaries of State in US history. Unfortunately on the other hand, his brand of "realpolitik"--working pragmatically towards concrete policy objectives without concern for ethics or ideology--meant doing things that prolonged and worsened wars, knowingly propped up autocrats and dictators, etc.

Objectively speaking, Kissinger was a powerful diplomat who accomplished a lot of what he set out to do. At the same time, just because you can do something doesn't mean you should, and a lot of us can only look back and judge him harshly for the long term effects of his decisions. Kissinger is the perfect example of a person who is highly intelligent and objectively effective at what they do, but because he had so little concern for simple human concepts like right and wrong, it's hard to look back at any of his "achievements" today with anything other than harsh judgement and disdain for the soulless husk of a man.