Good doctors who you can never reach and don't return calls.
It's like not having a doctor at all. Whenever I need something--like having a prescription refilled, an appointment on short notice, a referral, or a simple answer to a question--they just aren't reachable. As an extreme example (believe it or not), I called with severe symptoms one day, asked to speak to a doctor and was told that none was available. I am still waiting for the return call. I like the doctors, and respect their advice. I am moving to another practice, though, because their customer service is shamefully bad.