I forgot this: Impressions requires a lot of HW resources. Topaz should put the check HW applet up front, rather than embed it into the download or at the bottom of the screen. I've noticed multiple threads on their FB page with users saying it doesn't work with their HW because of an older version of GL and having problems updating.
Windows 7+ x64, OpenGL 3.2 is required.
One feature that is missing, when compared to Snap Art, is the ability to back off an effect in a specific area from within the app. Plus, it doesn't supply layers within the app. For example, in Snap Art, sometimes I want the background to be abstracted, the edges of flowers to be realistic, and the rest of the flowers to be Impasto with some fine tuning of brush width etc. I guess there is a way to do this with layer masks in PS/CC, but that means I have to have a workflow plan thought through, rather than making and seeing changes in real time.