According to the release notes it states: "
we have been running the application in the latest Chrome, Safari, Firefox and IE10 - we do not plan to support any older versions then those [sic]."
Based on my experience, this would mean almost certainly that we could not use Umbraco 7 for the vast majority of clients for the foreseeable future. It also means almost certainly zero adoption for anyone developing UK public sector websites. So it doesn't really matter how awesome it is, I can't imagine it being a viable choice for most development companies I know. Isn't this a shame?
I also think that even if we could offer it to clients, that most would find the UI more confusing than the older version. It may look more modern, but we know from Windows 8 and, to some extents, VS2012, that minimalism doesn't always equal usability, especially among the less computer literate. It feels too much to me that U7 interface has been developed by "hipsters" wanting to follow all the latest trends with too little regard for content editors (who invariably aren't hipsters or even good with computers). The old U6 interface icons may look ugly to us but I know from experience that people find it easy to use. It uses a paradigm that is familiar to a lot of people and is quite common across many CMS's.
Don't get me wrong, there are some amazing new features in 7 - such as Container document types. But I'd rather have basic stuff like an always-open tree, right-click access to common features and some better visual cues for what is going on. Maybe these will come, but then again if most of our clients won't be able to use it, then does it matter? I also think visually it's a bit, well, amateurish looking. It kinda looks like it's been put together by developers rather than designers. I'm presuming it's going to get a major polish at some point?
Sorry to seem negative, but sometimes I think people are rather scared of criticising Umbraco (for fear of upsetting all the hardworking people), and that's not always healthy.