In terms of location with respect to the city centre, this apartment was perfect. It's a short walk to the major tourist sites, as well as to the Staatoper, the starting point for many of the Hop-on-Hop-off buses, as well as a hub for public transit. Lots of great little places to eat in the neighbourhood. Eva and Michi were great about helping us out with a few things - and let us leave our bags with them on the final day (despite it being a holiday).
The apartment itself is very airy and clean. There is a huge discrepancy between the two bedrooms - the master bedroom with the double bed is immense, while the other bedroom is quite small, but if you're with friends then these are just places to sleep. The balcony is very comfortable and gets great evening sun.
The only downside to the apartment is the noise. The smaller bedroom gives onto a side-street and right across (at street level, obviously) is a nightclub. Folks come out of this club at all hours of the night - until the sun is coming up - and they can be extremely loud. If it's a summer night and the window is open to get some air, then you will definitely want to have some earplugs. The windows do a good job of containing the noise, but on a hot summer night, closing them is not an option.
I would recommend this apartment to someone who wanted something a little special in terms of location and comfort.