Worthy of Best Picture, NOT Director.
I will say that Kramer vs Kramer is the very best film of 1979. The subjects of divorce and parenthood are relevant now more than ever before. Plus the acting by the three main leads (especially by Hoffman) are virtually unbeatable.
But I will say that this was not worthy of winning the Oscar for Best Director. I know Best Picture and Director often go together, but this should have been one of those instances where they are separated. While I do think this was the best of the year, the general moviemaking really wasn't anything special. Apocalypse Now and Alien were 50x harder to create.
Best Director should go to the best movies that were the hardest to create. So movies like Kramer vs Kramer, Ordinary People, and Chariots of Fire should have lost that honour. And movies like the English Patient, Dances With Wolves, Born on the Fourth of July, and Braveheart were all worthy.