We used the express TGV on our recent trip. We were very happy with it, although it's obviously pretty expensive. But, not too badly priced compared to the regular train or shuttle bus which could take a lot longer.
The only ... negative is that the train is NOT designed to be an airport train. The "luggage" rack is extremely small and filled up pretty much immediately. That meant there was nowhere for us to put our luggage and we ended up standing in the doorway both trips with our luggage. And even though it is assigned seating, it seems to be a free-for-all. I offered to mind our bags while my husband sat down, but people were in our seats anyway (and in most of the other seats). Still, it's a very short trip (i.e. 9 minutes) so it's not a major issue. Just a little odd that an airport train isn't better designed to accommodate the expected amounts of luggage.