We were at Lake Isabella last year and the water was pretty low. If you go on the lake do so in the morning, anything after 1pm will be really windy. Just north of the lake is Kernville which is a nice place to visit. Don't eat at Ewings, terrible service and food. There is stocked trout fishing in the Kern River. There are a number of campground along the Kern River. Some are right outside Kernville, Camp James is the nicest one with hook ups in some sites. There are also a number of state campgrounds along the Kern River with only pit toilets and some with water. If you like hiking there is a nice hike at Johnsondale bridge that follows a fork of the Kern River, which is just north of Kernville. Even further north is a grove of giant Sequoias that are worth visiting.
If you are taking Hwy 178 out of Bakersfield be careful when you first enter the mountains. There are some really tight turns with narrow lanes and some large rock overhangs. It's only the first mile or so but it makes you wonder what the rest of the road is like. After that the roads are much better.