The vast majority of the time, the buses are just fine. They run as they should. Unfortunately, there are some who feel that buses should arrive as they are walking up to the bus stop, or that the bus should be there, waiting for them. And that isn't going to happen. Well...it can, and does, happen. But it's a lucky happenstance when it does. If you consistently wait about 10 mins for a bus, then you have no reason for complaint.
In my 30+ stays at WDW resorts, I think I've waited more than 20 mins for a bus only 5 times...and those times were at the parks, at park closing. I have waited just one time, for 30 mins, for a bus to DHS at Kidani!!! Now, I'm heading back there next month...so we'll see how the buses are then.
But, basically?? It's public transit. You just can't expect buses to come much more frequently than every 15 mins at the busiest times of day.