Our young family stayed at the Jolly for 5 nights in mid summer, having been strongly (and correctly) advised that pool & aircon were almost mandatory for travelling in kids in Italy at that time of year. We found it a pretty good value compromise. Basically you get the pool, ac & decent rooms for a good price. However you also get the pain of being well out from the centre of town: it's around 2kms west of the Vatican. Nearest Metro is a 15 minute walk up a hefty hill, so most residents stick to the nearby buses to get into town. These may or may not come quickly, can be hot in the summer, and will still take 15-20 mins to get anywhere interesting. Taxis are quick to arrive, but at 10 or 12 euros each way, get expensive fast.

Likes:
Quiet rooms: double glazed (yet openable) windows.
Well behaved aircon
Friendly staff throughout the stay.
Decent breakfast

Dislikes:

Pain of getting into the centre.
Expensive restaurant, with not much else close by.

The hotel is quite new and has very well appointed, clean rooms. Food is good as well.
The only problem is location. It is actually not that far from city centre, as you can get to St. Peter's and the Vatican by a single bus ride. However, as the hotel can be only be reached by bus or taxi, the bustling and chaotic traffic of Rome does make the difference. Timing is really unpredictable as a short ride normally taking 15-20 minutes may become a nightmare lasting over 1 hour at peak hours and/or inclement weather.
In the end, it is a very good business hotel. If you are visiting Rome for sightseeing other than cars and traffic, you should better search for a different option where commuting by car or bus to major attractions can be avoided.

Stayed for 4 nights. Good location away from the city centre. Travelling wasn't a problem once we had bought a bus map from the hotel shop. The room was comfortable and for a short stay the limited storage space was adequate. The only meal we had at the hotel was breakfast, which provided a good start to the day. I would be happy to stay there again.

Just back from 4 nights at the Jolly hotel Villa Carpegna. For the price we paid - €170 per night for a double b&b -( we got this rate from a discount hotel site- you can't get it from the hotel directlly as we tried) this hotel was very good value, especially seeing as it has a pool which the vast majority of Rome hotels don't.
Room was ok size, very nice bathroom, there was also a safe in the room. Lack of storage space though. To the hotels credit their website says the pool is only open in July and August, yet we were there in the first week of September and they kept it open, with lifeguard, even though there were generally only a handful of guests using it.
We slept very well as the room was far enough back from the road that we weren't disturbed by traffic noise.
The hotel is not too far out from Rome. Buses stop right across the road. Trastevere train station (on the line to Fumicino airport) was a short 10 minute (approx €10) taxi ride away. The train to Fumicino airport from Trastevere runs every 15 mins, €5.50 one way, approx 30 mins journey time.
Room service was quick though the quality of the food wasn't great. Food and mini bar prices were steep so we avoided eating in the hotel apart from breakfast. Breakfast was ok but not great.
Our food experience in Rome wasn't great overall. Food was very overpriced and very poor quality compared with what we had enjoyed on the Amalfi coast earlier in our holiday.
Taxis in Rome are a nightmare. They seemed to take different routes to the same places so the prices varied alot depending on the driver. Be very careful when getting a taxi from the Trevi fountain. On our last night we got into a taxi there. The driver didn't put on the meter. We queried this and he told us in Italian that it would cost us a flat rate of €25 to the hotel. We had never paid more than €17 for a taxi back so we said no. After arguing with him for a few minutes we ended up getting out of his cab, walking down the street and hailing a taxi that cost us €15 on the meter.
Overall though, Rome is a great city, with so much to see. Having been there three times at this stage and stayed in 3 different hotels, I would strongly recommend the Jolly Villa Carpegna and will stay there again if we go back for a fourth trip.