The above large embed might look sharp enough, but is not true YouTube HD. In order to view full HD, click play first, then click "HD" quickly at the bottom right. YouTube HD viewing experience is still buggy, as evidenced by the brief green screen when transitioning from non-HD to HD. Once you are in HD mode, try clicking on "full screen" mode, which is impressively sharp.
The footage of this video was shot on a sunny afternoon. Smaller embed: