Every time a Deepmind paper is published, I feel simultaneously very excited, and also very depressed that they keep speeding ahead while I'm not anywhere close to understanding their first paper about AlphaGo.
I recommend skipping the first AlphaGo paper, because it is completely superseded by AlphaZero and actually harder to understand.
I completely agree, the alphago paper is more like the working notes of a team that just accomplished something. The alphazero paper is a more careful analysis about the theoretical underpinnings and paints a clearer picture.