I need to try l'Epicure at le Bristol but it's supposed to be among the best experiences in term of food within Paris.
Alléno at le Meurice was oustanding but he left 6 months ago (to Le cheval blanc in Courchevel i believe) so I don't know how it has evolved.
Ducasse at le Plaza is a classical interpretation of a 3 star restaurant. You can't go wrong with this place, and I would advise it compared to Le Cinq at GV.
Le Royal Monceau used to have a wonderful restaurant with a "jardin d'hiver" and a harpist playing at nights but they scrapped it when they did the remodeling, and the new restaurant is a joke compared to before.
L'Abeille at Shangri La and the MO restaurant are not in the same league.

Food is a personal experience, so just my taste. However, there are some restaurants not within hotels in Paris that shouldn't be missed.