We did both a drop off and pickup from the Port Canaveral location. For drop off, you pull around back (to the left side of the building), they scan your car, and hand you a receipt. Then you just walk through the building and there is a small waiting area right up front with a couple restrooms where you can wait for the shuttle.
For pickup, we had a good experience but that might have been because we did self disembarkation as we were going over to Kennedy for the day and wanted to get out early. While we were not the first off the ship, we were still some of the early ones. When we got to the rental car location, we were one of two couples (us at Enterprise, the other at Alamo). They don't have any of the automated kiosks like airports, but the agent was fairly quick.
I will say though just after we got the keys, another shuttle pulled up and offloaded a good handful of groups. So really, I think it is all about timing.