I'll have to say I did kill him although my reason was mostly because that was the ending I most wanted to see. I also did not replay it, I think you should stand for what you have decided, as a comment to you Laurent
In general I think the game achieved what it was after, actually making you reflect on both the theme of the game and games in general. As a comparison I just played Fable 3 in which towards the end you have to make several choices none of which are actually good, just degrees of bad. The way those choices are portrayed reminded me of the final choice in this game, the fact that there is no right or wrong just choices to make. Like choices in real life often are. When choices are like that they for some reason strike a cord and actually matters, which from a game perspective seems wierd, that a more undefined, no right or wrong, choice "feels" harder to make.
Anyway, just some reflections.