We stayed at Mercure Paris Opera Cusset for three nights at the end of May. The hotel was very good: service was good and friendly, room was clean and comfortable. As always in Paris there was not excess space in the room but it was definitely big enough for us two. The room had a refrigerator and an electric water heater, which was nice. Room was also airconditioned and when the window was closed you could not hear the street noise at all - the hotel was very quiet in every way.
Location was good, near the Metro. Only thing was that when coming from the airport (Charles de Gaulle) you had to change from train to metro and then again to an other line. But this didn't take long and didn't bother us as we had very little luggage to carry.
The service was good and friendly, we were even able to check in earlier than promised, we arrived before noon and the check-in started at 2 pm. The staff spoke very good English. Breakfast didn't include and was quite pricy but we wanted to eat at cafes anyway so that was not a problem for us.
All in all: good hotel at good location. Would recommend.