Lunar Crater is DEFINATELY worth the trip to. It is decently marked with road signs. I went in September. You can see that the area is also DEFINATELY at risk for flash floods. You can see that in the terrain surrounding the area. There are places where you can see that water rushed over the road. Lucky for me, I went when there was no rain in the forecast :)
This is a isolated and rugged place. The road is OK....some parts of the road leading to Lunar Crater I was able to hit 45 MPH in a compact rent-a-car, but mostly it was slow. You have to be VERY ALERT if your gonna go 45 MPH on that 6 mile road leading to the crater. The road is rough in some places. I don't think it would be doable if the terrain is wet, even in a 4WD. Again, I drove there in a small car and had no problem, but everything was dry.
You can drive right up to the rim, and there is a sitting area at the vantage point. Nice. I noticed a road leading along the rim of Lunar Crater and drove it. That was spectacular. You could see for miles, and it is VERY ISOLATED and REMOTE back behind the crater itself, and I enjoyed very much exploring back there. Like time stands still.
I didn't actually hike down into the crater; I just enjoyed the vistas all around the rim, which as I said, is drivable. Have fun and enjoy this unique spot. Make sure your vehicle is good. And for heavens sake, make sure you get plenty of fuel at every chance you get. I was in panic-city on the drive from Lunar Crater to Ely, NV. When I arrived at Ely, I had 12 miles worth of gasoline left. Yikes!