Hotel Diocleziano is a very nice hotel. The room we had was on the first floor, just off from the main check-in desk. It was small, but comfortable and very clean. Oddly enough, the bathroom appeared larger than the room! There was also a cute little deck with a bistro set.

Some small complaints: The shower is tiny! And if you move the shower head so that it faces the area where you enter/exit, you will flood the bathroom, as the water goes through the curtain and the drainage system is slow. Hopefully it's something they will fix before the next guests stay.
Another complaint is there is some noise, not sure what it is, every morning. It's almost like some ice machine above or something. So if you're a light sleeper, or don't like noise, this may be something to consider. Ask to stay in another room.
Some people have written that you can go on the roof of the hotel and get a great view of the city. This is true, ONLY if you are a guest in the top floor room. That's the only access to the roof. So unless the guest staying in that room is you, or really friendly and let's you in, you won't be able to access the roof. Just felt I should make this clear.

Another thing to mention is that they only serve breakfast. No lunch, dinner or food available at any other time. Luckily there are several eating places nearby. I can't say anything about the breakfast buffet as we did not eat breakfast here. I also can't comment on the gym or sauna b/c I didn't even check it out, but I know they have one.

Perks: They leave you coffee, tea and other beverages daily. This was great. Especially after some long days of touring. It was nice to come back and have something easily available to drink.
It's so close to Roma Termini. A stone's throw away really. This was incredibly convenient!! It's also close to several eating places.
They exchange money for you at the front desk. And the rate is fair. Comparable to most other places.

I had a hard time giving this hotel an overall rating. It's definitely better than a 3, but not quite a 4. I've stayed in some of the best rated hotels in the world, so a 5 is something I don't easily give. I'd say 3.5 is about right. It doesn't have a lot of the perks that a larger hotel/resort does, but if you're looking for a very nice, comfortable, clean and conveniently located place to stay while you spend most of your days seeing what this great city has to offer, then this place will suit you just fine.

We had much helpful service from the staff in calling cabs, packing early breakfast for the airport, etc. Large bathroom was nice. Location 2 blocks from train station is very convenient. On a quiet street next to a museum park.

friendly and very accomodating staff, excellent breakfast before a long day sightseeing, very comfortable rooms, clean, tidy, spacious and a good sized bed would reccomend evryone and anyone to try this hotel if you are ever staying in roma, I would like to thank all the staff for making my stay in rome a very enjoyable experience.

You can't beat this hotel for location from the Termini Station just a 5 min walk out the front accross the bus station and main road. So the journey from Fiumicino is very easy by train just jump on the Leonardo Express and you are there approx 30 mins later (€14 per head each way).
The hotel is in a quiet road opposite the bus station but like any area with a large train and bus station it has its odd characters and with major building/excavation works opposite the station could be considered not the best part of town. The hotel/bedroom was spotless and well furnished, good size bedroom ours looked out over the front of the hotel and had shutters if we wanted to use them. Bed was large and comfy and bathroom modern and very clean. Breakfast provides a good variety of some hot and all the usual cold things (cereal, fruit, cheese, meats etc.). You can order freshly squeezed orange juice for free - recommended! Staff are very friendly and helpful and we got great service at their bar with late night drinks, the porter was also very keen to help with the cases and wasn't looking for money just to be helpful. I've also just received an email at home from the hotel hoping we had an enjoyable holiday and stay - nice touch. Great hotel, good travel location, just a pity the local area wasn't a bit nicer.