Editing appointments in iCal turned into something of a hassle when Apple decided we didn't need that slick little Inspector drawer any more. It turns out Apple left the Inspector in iCal, albeit in the form of a panel instead of the drawer.
To see iCal's Inspector panel, choose Edit > Show Inspector.
iCal's Inspector panel is hiding under the Edit menu.
The Inspector panel shows the the currently selected appointment, and you can edit the event's details without any extra mouse clicks or keyboard shortcuts. Since the Inspector is a panel instead of a drawer, you can position it anywhere you like, too.
You can view and edit appointment details in the Inspector panel.