You can create appointment slots right through your calendar!
Your calendar allows you to set goals.
Check out the Quick Add feature for your calendar.
Customize the colors of your different calendars so you can differentiate your events.
There is a weather feature in your settings!
There is a built-in To Do List feature in your Google Calendar.
You can subscribe to a variety of "Interesting Calendars" to keep track of holidays, sports, phases of the moon, and more!
Your calendar has a search feature (who knew??).