My husband and I found a great deal on Expedia at this hotel as part of a flight and hotel package, so we booked it for our honeymoon. We stayed for 9 nights and overall, I was very pleased with Blu Hotel.
First off, if you're looking for ambiance, look elsewhere. It's a pretty basic hotel, but still quite nice. The decor was nothing special, but the bathroom was huge (with a tub! So nice when you've been trekking all over the city!), and the room itself was a lot larger than I expected from a European hotel room. Another great feature was the room had a tile floor, not some icky, mildewy carpet that you find in a lot of hotels. We also stayed on the 1st floor (2nd floor to Americans), and had a really fabulous wrap-around porch attached to the room. It was really nice to step outside and watch the city waking up in the morning.
The biggest negative about the room was the bed, as it was not the most comfortable. I managed just fine, but it bothered my husband a bit. There's also a bit of noise coming from the hallways sometimes, but nothing too terrible. The doors to the porch kept the street noise out surprisingly well.
In the room there's a small TV, but only Italian channels and they're very limited. We'd hoped to have at least the BBC, since it was right after the election and I wanted to stay caught up, but mostly we ended up watching bad 80's cartoons in Italian (Anyone remember Sheera?). There's also a mini-fridge loaded with the typical stuff-- Coke, water, beer, etc. All for a ridiculous price, but it's there if you want it.
The hotel breakfast was decent, though nothing terribly special, and overpriced. It's convenient though, since there's little else around that area for food. The restaurant is okay, but again, nothing special.
Blu Hotel is kinda far from the metro, so if you're planning on using it as your main means of transportation, be prepared for a 10-15 minute walk crossing a few busy roads. It wasn't that big of an issue for us, but Rome in general requires a lot of walking unless you do one of those bus tours, so having to hike back to the hotel at night isn't so fun. Rome is VERY pedestrian-friendly, so the walk itself isn't terrible. I was also very happy to be able to burn so many calories-- I ate whatever I wanted because we walked so much! The closest station is Tiburtina, on the B line.
The hotel staff was a mixed experience. They all spoke English very well, which was a relief since my Italian sucks. The male receptionists were very helpful and knowledgeable, giving us directions to places all over the city. My only complaint was that one of the female receptionists was somewhat rude and seemed to be annoyed whenever we asked a question.
Overall, I think Blu is a great place for those on a budget that have plenty of time to see the city. We had a great time.
Pros: Clean (thanks to the most fantastic housekeeping staff!), mostly quiet, inexpensive and overall a pleasant experience.
Cons: not the most comfortable bed, somewhat far from the metro (but still very do-able to most)
General tips: If you're going to be using the metro a lot, buy a pass from one of the tobacco shops in the station. We used a machine once, and it ate 30 Euros worth of bills. Not so fun. Save yourself the hassle.
Also, Termini station is great for stopping for a quick bite to eat. There's a grocery store on the metro level, and we bought take-away meals and brought them back to the hotel for dinner. Saved us a lot of money-- 3.50 Euros for lasagna! There's also a bunch of fast food places (both ground level and metro level) and a Boulangerie (bakery) that has really great pizza (ground level, on the far end opening up to the street). The best food of the city is to be found at small, take-away shops, so skip the sit-down restaurants and go to the tiny, busy local haunts. You'll be happy you did.