Location cannot be beat! I read other reviews and was worried about the noise- with the windows open, it is very loud. However, the once you close them, you can no longer hear any of the street noise. I have a lot of trouble sleeping with any noise and it didn't bother me at all.
Shower temperature was not consistent at all (would go from freezing cold to searing hot in the matter of a minute), but I've come to expect that from these old buildings, so if you want to stay in a place like Trastevere, there are some trade offs.
Overall, I'd stay here again.