I've gotta say I've never been a fan of the WP themes, but twentythirteen is fantastic. I am seeing this from a (semi) developer's PoV, however. I like my bundled themes to be easy to create child themes from and this theme is very easy to do that. I'm not a great fan of the coloured page types but that's simple enough to change.
What I like about this most is the simplicity of the design. Stripped back to bare essentials, the user-experience is comfortable and uncluttered. I'm hoping this is indicative of future web design in general, where the emphasis is placed on content, and where design merely assists in the consumption of that content rather than detracting from it.
Nice work, WordPress.