On May 7 a friend and I stayed at the Rome Airport Hilton: http://www3.hilton.com/en/hotels/italy/hilton-rome-airport-ROMAPTW/index.html. We thought this would be convenient since we were arriving in the afternoon, going into Rome for dinner, and then flying out the next morning.
While the hotel is connected to terminals 1, 2, and 3, by internal passageways, it's quite a long walk from them. My friend felt it was too long with his large heavy luggage. I didn't mind as much, but my luggage was lighter. The only other airport hotel I've used was in Calgary, and that one was MUCH closer to the terminals than this one.
There is a free shuttle to Terminal 5, which we used the next morning with no problems. So, it was actually easier to get to T5 than T1.
WiFi and breakfast are not included and are very expensive. However, there is a tea and coffee maker in the room. The room was €209 for the night. It was nice enough, although not as nice as the Hilton in Short Hills, NJ (the only other one I've stayed in).
The hotel runs a free shuttle into Rome every two hours (leaves hotel on even hours, returns on odd hours). We took the 6 PM shuttle into Rome which worked well for our 7:30 dinner reservation. But we would have been rushed to make the 9 PM shuttle back and did not want to wait for the 11 PM one, so we took a cab. The driver wanted to use the meter saying it would be about the same as the legally required flat €48 FCO airport rate, but I "knew this was a scam" and insisted on the flat fare. Guess what - the metered fare (he kept it running to prove his point) was indeed about €46. So, he got a few euro extra from my decision. However, this was at 10 PM on a Wednesday night. During the day, traffic would have made the metered fare much higher, so the flat fare is the way to go.
I'm not sure I'd stay here again. It worked well for our needs, but it wasn't much easier than taking a cab between the airport and a central Rome hotel.