The type of gravel road will make a big difference in how much fun it is to ride. If its basically a dirt road with some gravel on it, those are a lot of fun. The gravel there keeps things from getting too boggy and those I enjoy riding. There is the gravel road where the gravel has been packed down very well and is almost pavement. Those are not bad either. The gravel road that is all gravel and all loose gravel to me is no fun. Watch the turns. With loose gravel it is common to turn the handle bars and keep going straight. No fun when a bike is pushing like a pig, but thats better than loose. Sometimes its the back wheel that lets go and you end up on the ground.
Trying to get the power down on loose gravel too is tough. Press the pedal too hard and the tires just spin. Everything must be smooth. As far as tires, wide tires usually work much much better. The bigger the contact patch the better within reason.