Stayed here for 4 nights in June as part of a trip around Italy. Having read all the reviews and having stayed at the Princess Hotel (just 200m down the road from Parco Tirreno) the year before I knew what to expect of the area, but was getting the impression that the hotel wasn't great.
Check-in was efficient and the staff friendly and polite. Upon entering the room, it was apparent that certainly wasn't anything special. Yes, the carpets were old and dirty, but the bathroom was quite clean, (although the shower was tiny) and it had all the essential amenities, such as a safe, TV etc. The bed was large, but was composed of two single matresses put together which made it only slightly uncomfortable- I was expecting it to be worse. The balcony was nice and it was lovely to sit outside at night.
As for the hotel itself, I was impressed at the lovely gardens surrounding it, in addition to the restaurant also allowing you to eat outside. The breakfast was basic but did the job, but the dinner was much better and I quite liked it. The hotel bar was quiet but nice in the evenings to relax in. The pool was large and made a nice relaxing afternoon, we paid 15€ for the two of us but I deemed it acceptable for one ocassion.
The hotel's location is slightly inconvenient but not terrible, as Cornelia metro station is a brief walk away and the metro gets you into town much more efficiently and cheaply than a taxi. There is, however, not much nearby as stated in other reviews, except a McDonalds- but I considered eating there to be a crime in Italy of all countries, as Roman food is exceptional.
Overall, I would say the really bad reviews about this hotel are inaccurate, unless you are used to 5 star luxury resorts, what you get for the money you pay is not bad, given that Rome is quite pricy. The rooms aren't great admittedly, but the hotel serves it's purpose and the staff and facilities are of a high standard. If I was on a budget I would stay here again.