In particular, I thought Redmond's handling of the top right corner was striking. He identified it as a potential attack for white several times before white's actual attack, and then afterwards thought that a move was 'big' that AlphaGo ignored; later, on calculation, he realized that it was only (if I recall correctly) a one point move.
It looked to me like an example of the human bias towards the corners and walls, combined with his surprise at some of AlphaGo's moves that made significant changes in the center.
There have been a couple of brief discussions of this in the Open Thread, but it seems likely to generate more so here's a place for it.
The original paper in Nature about AlphaGo.
Google Asia Pacific blog, where results will be posted. DeepMind's YouTube channel, where the games are being live-streamed.
Discussion on Hacker News after AlphaGo's win of the first game.