We recently returned from a three night stay in the Chateau Frontenac. In my opinion (which is not unique to myself), this is the only place to stay in Quebec City. The hotel itself is a site to see, the location is unbeatable, and it does feel like a Beauty and the Beast set. Our room was in a turret (seriously). The rooms have been redone (ours had a marble bathroom and updated furnishings). I was concerned that the hotel would be outdated and "banking" off of its location, which was fortunately not the case. We asked for restaurant recommendations from the concierge and she was quite helpful.
That said, please keep in mind that this is one of the top sites in the city. The lobby is incredibly crowded (completely understandably), as are the restaurants. The hotel does a good job walking the line between luxury hotel and giving back to the community with exhibits about its history (and the more pragmatic public restroom). But, as a guest, do not expect to have the place to yourself.