In my experience (as a Registered Nurse, a patient, or a relative of a patient) having a good GP is priceless and can make all the difference to your health and well being. Having a local doctor who knows your history well, and understands your concerns is invaluable, particularly if you have a chronic illness. BUT they can be hard to find.
Now no disrespect to the the medical profession, there are numerous committed and professional doctors available in the community, but sadly there are some that really miss the mark. I have witnessed first hand some unfortunate cases of GP's misdiagnosing a serious illness and the consequences can be devastating. I acknowledge it is a tough job, and they are called 'general' practitioners for a reason - they know a little about a lot of different things (apart from those who specialize in certain areas) - so we shouldn't expect them to be experts in everything.