It's a great appartment slightly outside of the city center. There is a tram stop right in front of the building that takes you into the center, to many of the sightseeing spots, and to the U2 subway stop that takes you directly to the Prater and the Stadium. Should you decide not to use public transportation, the city center can be reached by foot in about 15 min.
There is a grocery store right across the street; restaurants, specialty coffees, and a really nice Irish Pub (Charlie P's) are in easy walking distance.
The apartment was very clean, the beds are comfortable enough, and the host communicates well and frequently.
Really the only downside is that the windows can't be blacked out and the sun will shine into the room early. That might cut your nights a bit short - but eh, you're there to explore and not to sleep anyway, right? :-)
Definitely highly recommended and a very good alternative to the overpriced stays in the center!