The JW Marriott in Cannes is a very nice hotel and extremely well located, however the price of the room we stayed was nowhere near where it should be, far too expensive for what it was.
Nice room, comfortable bed and good shower, but a mix of staff friendliness, some really nice some not at all, no window opening, no balcony, and it was not clear at all when we took the reservation. It looks like many rooms in this hotel have similar set up, so be careful to this.
Overall, and we travel a lot around world, we estimate my wife and I that we paid double of what it should have cost us given the overall quality of what we got.