Well, they can go back to the drawing board and do some more research. This was an example posted here a few weeks ago, by a heavy Calendar user. Look at the old and new app and see if you can answer a common question for a calendar user, like when do I have some free time in the next month: http://imgur.com/a/Qo91p
Also, not that it matters, but the old app is 2 MB and works flawlessly, the new one is more than 20 and chugs a bit when scrolling on a quad core processor.
It's also become incredibly difficult to scroll properly in the new calendar. I constantly find myself scrolling horizontally when I want to scroll vertically, or vice-versa; it is maddening.
If they put colored sections indicating appointments around the circles in the latter example, as if they were 24h clock faces, it would be even more useful than the first example.
Also, not that it matters, but the old app is 2 MB and works flawlessly, the new one is more than 20 and chugs a bit when scrolling on a quad core processor.