Twenty Ten was great in its simplicity. Twenty Eleven was somewhat cluttered and filled with extraneous bulk. Twenty Twelve has gone back to the minimalist roots of Twenty Ten and taken things a step further by simplifying and de-complicating everything. Because of this it is a great parent for child themes. But that's not all. The extremely well documented theme files also make the theme an excellent starting point for people wanting to learn more about how to build themes and it sets a new benchmark for simplicity and minimalism where coding is concerned.
The one major drawback of the theme is the lack of support for IE8. Though this looks to be fixed in the next version, the real problem here is the reasoning behind the decision to not make it IE8 compliant. This was not a case of lessening the quality of the theme, but rather one of jumping ahead of the curb and leaving those cursed with IE8 in the wake. It is unnecessary and sets a bad precedent. Whether politically motivated or just the result of an oversight I hope that future theme releases will take a less extremist route. But like I said, this is a small hitch that looks to have been resolved.