I stayed here over the Easter break and thought that I'd share a few thoughts as it doesn't look like anyone has written about it before.

The location of the Chateau is the big selling point. It's just 20min from CDG, but sits in its own little forest with a great view of over the countryside. Rarely is it so convenient to get out of things
The Chateau itself is pretty on the outside and reasonably nice on the inside. The architecture is pretty and there are multiple terraces already setup for outside dining and drinking which I am sure in the summer is lovely. Inside, the Opera Restaurant is a stunning room. Other parts of the hotel (including the rooms) appear smaller than in the photos on their website. It is nice they have a spa, but it again wasn't quite as nice as the photos suggest
Food was reasonably good, wine selection mediocre, cocktails look good on paper but were made by staff who clearly had never received the proper specs (e.g. Bellinis are served by the half pint)
Over Easter, clientele were exclusively French - primarily well to do Parisians, if the amount of French designer brands was anything to go by
The hotel has no understanding of what a Hyatt booking is. I wasn't considered for an upgraded room (I'd generally complain, but have you ever argued with a Parisienne?) and I had to push hard to get breakfast removed from the bill
It's hard to talk about value for money going into 2023 summer where few places seem to be under €1K a night. At €500 a night so close to Paris, I don't feel that I was being ripped off

Overall, a pleasant enough stay but I can't see myself wanting to return.