Congratulations AlphaGo!
Some quick thoughts after game 1 (I watched the game on and off so this is not a thorough impression):
1. Lee clearly seemed to underestimate AlphaGo when he went strait to fighting very early in the game.
2. AlphaGo's evaluation skills seemed even better than Lee. It felt like it didn't miss a single weakness in both of its own and Lee's position, and incorporated it into its strategy. For example, the well timed probe at j8 in the middle game was quite impressive in itself, and the follow up after that - allowing Lee to create a huge, near-territory like moyo in the lower left, while building a long but useless-looking (at least territory wise) wall in the right side - looked a bit unreasonable at first, but it opened up so many possibilities in the right side so was not that bad after all (in fact, it was there where it was able to gain the lead in the game).
Its use of aji was very good throughout the game - a hint of how much it regards the value of hidden potentials, which I think is a sign of extraordinarily strong intuition formed from a vast amount of experience. Lee's strategy of making the game complicated didn't work out for him - because AlphaGo's strength in chaotic fighting was just as good (if not better) as Lee's. Especially AlphaGo's move 102 seemed to shock many pros, including Lee.
It also seemed to play a lot of unexpected but surprisingly effective moves. So much for human creativity.

3. The Korean pros commenting seemed pretty clueless of how computers tend to play. For example, during the game AlphaGo made a couple of "mistakes" according to them - because it seemed to lose points locally - but in the end those "lost points" were quickly recovered somewhere else, or didn't matter in the end. Anyone who played computers a lot will know they tend to start 'losing points' once they think they're ahead - right until they win precisely by half-point. It gave the impression that AlphaGo is a lot better than pros in positional judgement.
4. I think Lee held out well overall, but (according to pros) a single mistake in the lower right corner was enough to lose the game. If that's all it takes to lose, then AlphaGo's strength is scary indeed. I expect a 5-0 victory for the bot.