Lots of things have changed in BaseCamp 4.0. It's sometimes hard to know what one bullet point in the change list means, which is why I am breaking down some of the changes and try to illustrate it with some screenshot, when appropriate.
New Features
Garmin Adventures!
Basestation Mode for Astro and Rino

You can now connect your compatible device to BaseCamp and see your position live on the big screen in BaseCamp. You can also see where your dogs (Astro, Alpha) or buddies (Rino) are. Firmware updates for Rino 6xx and
Astro 320 should now be available.

You can now plan your trip better than ever by adding departure, layover and arrival times.

Right-clicking on the map with the hand or pointer tool selected will now give you options.