Good, not great

I give it 3 out of 5, why ?

The rem thing alone already turned me off, couple that with the mobile-first-attitude, and that takes 2 from the 5, otherwise it’d be big 5.

These are 2 references to the usage of rem in the head of Twenty Twelve’s style.css

---------- Further reading

https://snook.ca/archives/html_and_css/font-size-with-rem
https://blog.typekit.com/2011/11/09/type-study-sizing-the-legible-letter/

Now, please go “take a look” at Jonathan Snook ‘s own site above, he doesn’t even use rem he uses px and the blog at typekit too, it uses px

Since when that WordPres’s default theme is for testing new and un-proven technology for the rest of the world ? Why WordPress take the plunge for them ?

Here is the link that I think it might be useful for 2013 defaut theme’s development.
https://alastairc.ac/2012/04/relative-pixels