Three things got me:
AlphaGo was able to access the online games of people who do this - 90 million of them. If you think that the top player can probably watch a few thousand games play out over their lifetime it starts to boggle the mind.
In early training on Space Invaders, Breakout etc. they simply left the computer to play itself overnight, relying on reinforcement learning (if it works, remember it). On the first day it knew nothing, by the second it was as good as most people, by the third it was ahead, even coming up with ways of winning, people haven't thought of. If you think of how many computers there are in the world sitting doing nothing, imagine the resource we are wasting - SETI on steroids.
Third was the ambitious aim - Solve intelligence, then use intelligence to solve everything else. Soon we have, in the words of HG Wells, "Minds immeasurably superior to ours" to work on every problem. Cool!