I stayed at Mercure Piazza Bologna for 3 nights with my boyfriend. It is a fantastic location. It is 2 stops from main train station which is right in centre of Rome. The hotel is lovely. Not much character at all but is a great price (327 euro for 3 nights double room)for decent hotel in mddle of Rome. Locality was quiet, very safe and people were friendly. Was 11 euro for taxi from Corso-hotel which is not bad at all!

Breakfast was horrible. We ordered room service night before. It said it was continental breakfast-bread was a bit too chewy for my liking ' selection of fruit and yoghurt' included one wrinkly apple and pineapply yoghurt. Apart from breakfast, I couldn't fault the hotel. Staff were friendly enough and quite helpful!

Had fantastic stay in Rome. Would definitely stay at Mercure again because of price, cleanliness and proximity to city centre.

Make sure to try tiramisu ice-cream gorge! Fontana di Trevi takes your breath away-so beautiful!

Stayed here for three nights in August as a 'cheap' option to the expensive city centre hotels (website rate 100Eur per night).

Modern hotel (typically Accor) - everything works and is clean and just what you would expect from 2/3*

Staff very friendly and helpful (and English-speaking!)

Didn't eat in hotel so can't comment on food.

Bathroom in my room was very small and not comfortable.

@JunuTrivedi's comments below are mostly incorrect. It's not the hotel's fault the airport is 19 miles out of the city! The hotel is only three stops from the main railway station on the metro and DOES have escaltors and lifts (I managed my heavy baggage just fine!) It's a short five minute walk from the Bologna Metro station to the hotel through a very safe residential area (I walked it at 5.30am).

I would prefer to stay more central but you will pay for that!

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 ?