We love Donald's! We've been 5 times and had a great experience every time. The character interaction has always been good. We've had some servers that were more talkative and funny than others, but the service has always been good.
The food is typical breakfast buffet food, but it has always been fresh and well-stocked.
Four of our five trips, we've gotten the first available PS time (either 8 or 8:10 depending on the policy at that time) on a non-EMH day so that we were just finishing breakfast about the time that the park opened. The other trip we had breakfast at 9:30 on an EMH day. The service and character interaction were the same both ways, we just preferred dining early and finishing up when the park opened.
It can get pretty crowded and loud at Donald's, but that's never affected our experience there.