I've got an s3 and a nexus 7, so I can compare both in the long term. Touchwiz is not a bad product, though it adds actually very few to stock experience.

The main problem is that for such minor enhancements, you are condemn to be always late in android updates.

We are now fairly aware that updates are not only about getting new features and bugfixes, but also are the main mean to avoid security breaches.

If OEMs don't get that, what to expect if they build their own OS ? Not saying it will be bad, but they'll have hard time to alleviate my worries about that.