It is very easy to reserve parking, and the process of parking is very simple and easy to understand. Usually the wait for a shuttle is minimal, and most of the drivers are quite friendly and helpful.
We've used The Parking Spot since 2011. We've liked the rapid pickup at parking spaces, etc., but we've only used the new Standard/Basic system once and are undecided.
Your service is easy to book prior to travel. Wait times, leaving the lot and coming back, are very reasonable. The drivers are polite and helpful.
One note, I did see someone needlessly take an extra round trip to the airport because the explanation of your airline is on the other side (without the explicit statement that you should walk to the other side because the shuttle wasn't going there) was unfortunate.
I won't hesitate to book again!