And by "sharp" I mean both that the building is really slick, in a "this is what the year 2000 will look like!" way that we thought in 1992 or so, and that the building is actually sharp. It's made entirely out of metal and glass, and they didn't sand down the corners, so if you have small children, or are prone to drunken stumbling, pack some Band-aids. The building was designed by someone who clearly has never actually lived in an apartment. It is, however, very good-looking.
The apartment was spotless when we arrived. Kitchen is quite usable. The beds are super comfortable. The apartment is really a 1-bedroom, and they've put a second bed where the nominal living room would be, and the living room area is in the master suite. So, weird layout for hanging out, but you should really be out and about in one of the world's great cities, and not sitting in your bedroom, right? The bathrooms are great (2nd bathroom is toilet only, no tub or shower). The only thing to note is that the apartment is situated on an east/west axis, with floor-to-ceiling windows at either end. So you get the sun both coming and going. Don't forget to close the shades on the west side before you go out for the day; otherwise, you'll rapidly discover that the little glassed-in porch area on the west end of the apartment is like a magnifying glass.
Location is right in the middle of Mitte; easy walk to the two malls in Pottsdamer Platz, and both the S-Bahn and U-Bahn (U2 line) are easily accessible, so realistically at this location you're only a few minutes from pretty much everything in central Berlin, and only a few more minutes to everything else. Most of the restaurants in the Sony Center itself are mediocre and overpriced; basically the German version of Applebee's. But get out in the city to find the great food for great prices you hear so much about. The area around Sony Center is like pretty much any large city's downtown: chain stores and restaurants that you can see anywhere. You aren't going to Berlin to shop at TJ Maxx and eat at Tony Roma's, are you?
The nearest grocery stores that I could find are in the basement of the Mall of Berlin. There's an Aldi's and one other I forget, but which was much nicer than Aldi's.
All in all, no complaints whatsoever. I would definitely recommend this flat if you have business in the downtown area, especially for a shorter stay.