A friend and I were in Normandy earlier this month. I have to admit I was a little nervous about driving around CDG, so I connected at CDG to Rennes, picked up a rental car there, and made a stop at Mont St. Michel on my way to Normandy. At the end of our time in Normandy, we drove to Rouen, dropped off the car at the train station, and caught a train to Paris.
We stayed at an amazingly cool B&B (B&B les Oiseaux de Passage) in Isigny Sur Mer. The Guest House is a renovated centuries-old stone barn that has been lovingly and modernly decorated by the absolutely delightful hosts. We enjoyed the country lane location, but if you are looking to walk to dinner, Bayeux is a much better option.
We did the two-day American Experience Tour with Paul Woodadge, who is based in Bayeux and whose company is named DDay Historian Tours. We absolutely loved it. The first day was made up of Utah Beach and US Airborne sites. The second day included Omaha Beach sites, the La Cambe German cemetery, and the Normandy American Cemetery. The tour was an excellent (though emotional) experience. Paul is not cheap, so he is a fairly terrible choice for the casual tourist who is looking to check off a list of sites. But he is an excellent choice for anyone who wants to truly understand what happened at D-Day or anyone who is well-read on the topic and wants to see some of the less popular (but more meaningful) sites in Normandy. For me, this tour was money very well spent. For anyone interested, he has a nice "Recommended Reading" page on his website.
We found the Airborne Museum in Saint Mere Eglise (part of our tour) and the War Museum in Caen (not part of our tour) particularly impressive. And of course, the Bayeux Tapestry is pretty much a must-see.
If you can squeeze out a few more days in Normandy, I would recommend it. I would definitely recommend doing a tour of the D-Day sites to help you understand what you are seeing -- try to do a 2-day tour if you can swing it. I will definitely go back to Normandy and will spend more than this trip's 4 days there next time.