We stayed at Mercure Piazza Bologna for two nights as a pre-cruise stay. It is an Accor standard hotel, modern and comfortable. The rooms were not big but I wasn't expecting them to be big anyway. We had buffet breakfast at the hotel, good quality but not much variety. We had dinner once at the hotel because we were just too tired to go out for dinner (there were not any nice restaurants near the hotel). They only had one type of salad and ham&cheese toasts. Although both were good, we would expect it to have more options (in the elevators it was stated that the restaurant had a wider variety).
The hotel is located 5 mins from Piazza Bologna underground station, which is 3 stations from Termini (which is connected to Fiumicino airport by Leonardo Express). However, if you're carrying heavy luggage, you might want to consider taking a taxi (it cost us 28 eur for 4 ppl and luggage from Termini).
Overall it was a good option. We just felt we would have benefited from a more central hotel, which would have enabled us to rest for a while around lunch time and thus avoid the hot sun.

We booked the hotel on the hotel website on the assumption that a respected international chain like Mercure will be reliable in their descriptions and the price will be justified. We booked for 5days at an average rate of Euro 170 per night (without breakfast). Reaching the hotel wasn't easy. We arrived at the airport, then took the train to Stazione Termini where the change to the Metro line was horrible especially if one has luggage. The Metro station is a long walk away and the stations have several stairs and no elevators. After reaching the Bologna stop, we had to drag our luggage for quite a while and ask for directions before we reached the hotel.
The hotel itself is clean but very mediocre in terms of space and facilities. It is in the middle of some residential area and not really as 'close' to the centre as the Mercure website would like us to believe. The staff was pleasant but didn't really help. There was no one to help with luggage either.
All the above troubles would be fine if we were not paying the kind of tariff we did. It was just not worth Euro 170. Maybe, Euro 80 would be a good price for such a hotel.
After staying one night here, we checked out spent the next day looking for hotels near Stazione Termini and found a great 4 star hotel. Here we paid only Euro 165 a night and had breakfast included. The hotel was very clean, the rooms and showers were large and it looked every bit of the 4 star hotel it promised to be. And, the best thing was that this hotel was bang in the middle of the centre and 2 minutes walk from Stazione Termini, very well connected to all the places of interest, very close to nice eating places and full of activity.
So, why should anyone pay so much to stay at this far away and average hotel called Mercure Rome Piazza Bologna ?

This Hotel is located close to the Metro in a residential part of Rome. It's only a few minutes walk from the station but is a little tucked away . We spent the night before on a train and so arrived early at about 9am to leave our bags and were amazed when we were allowed to check-in and go straight to our room. The rooms were decorated in a contemporary fashion, were large and quite modern. The bathroom was of a high standard also. We got a great rate by booking directly through the Accor web site the day before. We loved the fact that this hotel is not in the tourist quarter and hence there were some wonderful little cafes and bars nearby. We had a fantastic meal at the little pizza restaurant nearby and can thoroughly recommend the bar/cafe/gelato parlour that is in the middle of the roundabout across from the Metro station. This hotel was one of the unexpected highlights of the trip-a quality hotel, at a reasonable price, in a great location.

My parents and I stayed at this hotel while we were visiting Rome on holiday. I had searched for the best prices, and found that it was actually cheapest to go via the hotel's website, although web rates meant that no amendments could be made.
We had a triple room (1 king sized and 1 single bed) and based on the hotels I have stayed in Europe, the Mercure Bologna had very large and comfortable rooms. The room was very clean and comfortable, and provided a welcoming place to relax in after a long day of sightseeing. The web price did not include breakfast so I can't comment on that, although when I saw another person's room service, the quality of the food looked good.
The hotel is situated on the blue Metro B line, and is 3 stops from the main train station, Termini. To get to the hotel from the Bologna Metro station takes about 5 minutes, and there are lots of shops and restaurants in between.
There was no air-conditioning in our room, but as the weather was quite cold, that wasn't an issue.
It is a comfortable and clean hotel, and its close proximity to the main tourist areas made it very convenient to get back to. Adding in the reasonable web prices, this is one of the nicest hotels I have stayed in Europe. My family and I enjoyed our stay in Rome, and enjoyed the hotel very much as well.