Several things I thought were interesting:

1. The commentator (on the Deepmind channel) calling out several of AlphaGo's moves as conservative. Essentially, it would play an additional stone to settle or augment some group that he wouldn't necessarily have played around. What I'm curious about is how much this reflects an attempt by AlphaGo to conserve computational resources. "I think move A is a 12 point swing, and move B is a 10 point swing, but move B narrows the search tree for future moves in a way that I think will net me at least 2 more points." (It wouldn't be verbalized like that, since it's not thinking verbally, but you can get this effect naturally from the tree search and position evaluator.)

2. Both players took a long time to play "obvious" moves. (Typically, by this I mean something like a response to a forced move.) 이 sometimes didn't--there were a handful of moves he played immediately after AlphaGo's move--but I was still surprised by the amount of thought that went into some of the moves. This may be typical for tournament play--I haven't watched any live before this.

3. AlphaGo's willingness to play aggressively and get involved in big fights with 이, and then not lose. I'm not sure that all the fights developed to AlphaGo's advantage, but evidently enough of them did by enough.

4. I somewhat regret 이 not playing the game out to the end; it would have been nice to know the actual score. (I'm sure estimates will be available soon, if not already.)