Drove around for the day, made it back to drop off the car in Caen and back to Paris for the night. I liked not having to drive around Paris, and driving around Normandy was not bad. In fact it was really fun, not stressful at all. Unlike my adventure driving around Scotland, but that's a story for another day.
We were young and full of energy. I would take it a little bit slower the next time. I'd love to hire a guide like Dallascoug said, but that's not something my wife is into. So books and pictures it is.
We really liked Mont St Michel - we hadn't been to a place like that before. We lucked out and were not there when there was a ton of other tourists there, which I imagine would detract from the experience a bit.
You will love it. Amazing part of the world.