If you just need a place to sleep at and nothing else, this is a 5* hotel. The room is the best I ever had.
If you want more than a sleeping place, and a full 5* hotel with proper Spa and Gym and the service with it, the Fontenay is sadly a disappointment.
My experience might be heavily personal but I still think it speaks enough about the hotel in itself. We were there with my girlfriend for 5 days, and the sauna was broken the entire duration of our stay. I understand that those things can happen but the explanations we got changed from one person to another, which just made it seemed that they had not idea what was going on, and did not bother hurrying up to fix it. Their compensation was a champagne bottle that we had to send back since my girlfriend is pregnant and cannot drink alcohol. That was all the hotel did for us, and probably for the other complaining guests, so you can understand why I feel the Fontenay is not worth 5*.
The gym is also too small, it is probably half the size of one of their room and is simply lacking equipment for those who want more than just running on a treadmill.
It is a shame because the hotel is beautiful inside and the rooms are incredible, but it does not compensate its other weaknesses.