I have to say that I like the new Snagit 12 interface. I prefer darker interfaces over lighter ones. Less pixels lit up means less power consumed on your laptop, for example. It also means your screen isn't so bright all the time (Office 2010+, I'm looking at you). They also make your content the visual focus instead of the application GUI.
However, I really don't like the new workflow. I believe others have commented about basically the same concerns. The changes to how profiles are used is particularly problematic. Why doesn't Snagit 12 capture using the last used profile when starting a capture with any of the default capture initiation options (Print-Screen, Start Capture menu item or Start New Capture button)? It seems to me that the main idea behind profiles is to streamline the capture process. Not reusing the previous profile runs completely counter to that. I have used Snagit 11 and earlier for years and have depended on this feature to save me from having to assign numerous difficult to remember hotkeys to my profiles.