We just returned from the Merulana. As noted by others, it is an odd little hotel/B+B. There is an attendant on duty every day from about 7:30 am to 3 pm. She sets the breakfast in the morning and then proceeds to clean all the rooms herself.
We had the inn book a car for us from and to the airport. It was 60 euros each direction. Expensive perhaps, but probably not much more than a taxi - with the added benefit of the driver knowing exactly where to take us and the inn knowing exactly when we were arriving. I highly recommend emailing them after booking your room and arranging a pick-up. Just to illustrate how helpful that service was, my luggage didn't arrive in Rome when we did. I had to wait in a baggage office line for 90 minutes, with no way of informing the driver that we actually had arrived. We fully expected him to be gone by the time we exited the baggage area, but he was still there waiting for us. (My bag arrived at the inn the next morning.)
The hotel belongs to another hotel nearby, which is listed in the folder that will be waiting outside your room when you arrive. Some other travelers have stated that the phones don't work - they do, you just have to know how to dial. Keep at it - you'll get it (dial two 0's before the 6, even though you might think you have to dial just one).
There is no reception, just a cold marble entrance behind a big wood door. The building contains businesses - it's an office building, not an apartment block. Only the 3rd floor is a hotel. You'll likely not see anyone else there.
The elevator is ridiculously small and ancient. Please remember to shut all doors when you exit the elevator, otherwise no one will be able to call it from other floors.
Breakfast is terrible. The juices are all made from powder (the red liquid is NOT tomato juice, but rather a powdered berry juice). There are cold cuts and cheese, a syrupy fruit cocktail and a couple of types of cereal. You can also make toast in the world's slowest toaster. The coffee is horrible, so ask the attendant for a cappuccino instead. She's very helpful and happy to make it. Ten times better than the instant coffee in the Thermos jug. There are only 5 tables (seating 2 each) in the extremely small and narrow breakfast room. It really wasn't terribly busy, so we had no problem finding space (family of 4).
Now on to the good stuff. The rooms are clean and modern. They have great HDTVs, but there aren't any English channels. Thankfully, the Beijing Olympics were on when we stayed there, so not much English translation was needed. There isn't a lounge, or a bar or anything. If you're a night owl like myself, you'll have to go elsewhere or give in and just go to bed early.
The aforementioned attendant (a very nice young lady at the time of our stay) could not have been more helpful, but, as stated above, she was gone by 3 pm. At that point, big brother in the mothership hotel a few blocks away was watching on all the carefully placed cameras. No matter when you arrive, you'll be let in remotely - either by the attendant from the 3rd floor, or a clerk in the hotel a few blocks away. You just have to use the intercom and all should work out. If the attendant is gone when you check in, your room keycard will be posted outside your door. After that, you'll have your keycard and will be able to let yourself in downstairs and on the 3rd floor whenever you like.
In the area - stay away from the restaurant directly across from the big church (Santa Maria Maggiore - read about it on Wikipedia - it's remarkably important) just around the corner from the Merulana on Via Carlo Alberto. The menu is great, the food was really good, but the prices are stupid. Instead, there is a great little unheralded restaurant the other direction down Via Merulana. It's called Tempio di Mecenate and it's located at Lago Leopardi 14-18 (close to about #60 Via Merulana or so - on a small side plaza next to Panne d 'Arte - a fabulous bakery). Tel. 06 4872653 - although you won't need reservations. They have an extensive Sardinian menu. The service is excellent and the prices are great. We found it completely by chance and ate there three times during our six day stay.
(Note - the stupidly expensive restaurant is open from 5 am until 2 am, so it has that going for it, whereas Tempio di Mecenate may only be open for lunch and dinner.)
There is another good restaurant almost right across the street from the Merulana (half a block away facing away from the church). It's called Scoglio Di Frisio (256 Via Merulana) and serves mainly seafood and pasta. It's an ancient, family run restaurant that's kind of cheesy (grotto theme, guy strolling around the restaurant singing cliched Italian songs like O Sole Mio and Volare - but he has a great voice and brought my wife to tears). The sole is about the best I've ever had anywhere, anytime.
The lowdown - would I stay there again? Probably, but I'd keep my expectations realistic. We paid 160 euros a night for the family "suite" (basically two adjoining rooms). That's a pretty extraordinary price in Rome for two rooms. To get the same in a more traditional, fully-featured hotel would have cost twice as much. If you don't expect more than a simple, clean room and a simple, unappetizing breakfast, at an extremely reasonable price, you won't be disappointed.