The built-in calendar app in Windows Phone does not have too many fans, but if it looked like Chronos Calendar that may be very different.
Seemingly cribbed from another operating system, the UI does not owe much to Metro, but it does offer one click appointment creation, a combined month and day view (but strangely no week view) and synchronization with your built-in and Windows Live Calendar.
Due to API limitations the app can not create appointments directly in your calendar, but it can write to your Windows Live calendar online, which will of course get synchronized back to your phone.
The app is both free and ad-free, and is worth a try for those who are tired of the stark lines of the built-in app.
Find it in Marketplace here.