Continuing My Observation

What details do you notice that you previously overlooked?
The quality of the audio on such systems is usually so poor that people simply pass on the ability to talk to the visitor and simply buzz the stranger in, which sort of undercuts the purpose of the system to begin with in terms of security. While many upperclass people can afford doormen, there should be a better system that eliminates the need for a human and I know it can be done cheaply.

What parts of the transaction seem fluid or effortless?
Opening the door. And that's about it.

What parts seem to take the most effort? What parts seem the most awkward or strained?
Everything else. For the visitor: finding the interface, learning the interface, learning how to respond to the audio, opening the door before the buzzer expires. For the occupant: listening to the visitor, trying to explain to the visitor what to do, giving enough time to allow the visitor to open the door during the buzz.