When you open up SharePoint Designer Beta 2 and try to edit a site, you will find that the code view is not there as usual even though you have full permissions of this site.

By default, SharePoint Designer uses the Contributor Mode, and you will be in the Content Authors group, this will restrict you to use some features. But if you have enough right on the site, you will be able to change the Contributor Settings or disable the Contributor Mode.

Click "Site -> Contributor Settings" menu of SharePoint Designer:

Hope it helps.