Interesting, a lot of people seem to be complaining but no one can answer why it sucks or what they hate?
I love the aesthetics in the new calendar, and my only complaint would be losing the month view with list of events below. But I use fantastical quite a bit so it doesn't bother me much.
The calendar stinks and here's why.
When you select a day it goes to that day and all I see is a 6 hour window. Before I could press the day and it would list my scheduled appointments at the bottom. I could see I had a lunch meeting and an 8pm call so instantly I could see where I was unavailable. That same task in iOS 7 requires me to have to scroll through the entire day to verify my appointments.
Now if we are ONLY talking about tomorrow, no big deal because I can pull up the list and see it or only have to scroll through one day. However if I want to quickly cycle through Monday Tuesday Wednesday this week next week and the week after it takes much longer and it is tedious. When I'm scheduling meetings with people I am instantly slower at responding for available dates.
You might like the new calendar because the changes do not affect you but it is not better than iOS 6. I'm not saying I want it the old one back, but I'm calling a spade a spade. It is worse and they will should do something about it.