I want to preface this by saying that these are relatively minor issues with an otherwise wonderful place, which I will be happy to stay at again in the future. It's a great bargain for that price. But if I'm being nitpicky...
1) Noise - My room was next to reception and I heard every conversation, door closing, etc., as if it was right in my room. If you're a light sleeper, bring ear plugs. If you're on your honeymoon or just want to feel quiet solitude, maybe pick another place to stay.
2) No cell reception in my room at least.
3) Weird smell sometimes, figured it's related to cleaning chemicals rather than sewage/mould. Open the window for 2 minutes and it's gone.
4) No safe, simple lock, no bars on windows = not for paranoids. I have to say I nevertheless felt very safe there.
5) The elevator is tiny and the doors have to be opened manually. A bit tricky with huge bags, but not impossible.
6) Beware, the city tax must be paid in cash and in advance. Not unusual in Italy, but best to know beforehand.
The #1 drawing point of Gialel is the affability and helpfulness of the owners/staff. They're kind, lovely people who will go out of their way to help you. Not everyone speaks great English, but there's usually someone there who does, and if not actually there, can be reached on the phone.
The second best point would be the location. About 10 minutes' walk to Termini, less than that to Barberini. Within walking distance (1-3km) of most major sights. Meters away from a kiosk, 3 minutes away from a supermarket.
The place is generally very clean and tidy. My room was cleaned daily. A couple of times there were stains on my towels, but they were clearly freshly washed ones.
Per special request in advance, I was given a kettle for the duration of my stay, at no extra cost. The room also had a mini-fridge and a hairdryer.
Pretty roomy shower (rare in Italian B&B's), with plenty of hot water (unless you want to shower straight after your neighbors, in which case they're a bit slower to come, but still there).
There is free wi-fi that I had no problem watching youtube vids on my phone with.