As the conclusion (for those who will not read all), for this price the apartment (and its great location) is very good. Photos and description are 99.5% correct (coffee machine was absent, the rest is 100% as on photos and description). There is no ideal apartment and this one has a few minor details (which might be not obvious).
Location: is excellent. About 100-150 meters to several lines (U7, S1, M19) and about 300 meters to S2, S25, S26. In most cases it took us 10-30 minutes to get to the place that we wanted.
Also, it was important for us: within 50-80 meters there is very good playground for children, quite big, with slides, climbing, water and sand.
And, there is a market (about 300m) where on Wednesday and Saturday we could buy fruits and vegetables cheaper than in supermarkets.
The apartment is on the first floor with door/windows to the courtyard (not to the street) - and that is great, but: if you keep window open - you will often here noise from suitcases in the courtyard (travelers going here and there). Also, thrash containers are rather close to the windows (I think, about 10 meters) so sometimes (not always) you may feel they are full :). And, be ready to meet insects - not much, not constantly, but they are (flies and mosquitoes). I must say that there are some repellents on the floor in the corridor and every room so the host is aware of this problem and has some actions against insects undertaken.
One room is very small and should be considered as a bedroom only (large bed to sleep and clothing rack).
Kitchen is quite good. It has excellent stove and oven (but unfortunately no ovenware - we could use only oven-tray). The host promised to bring frying pan and coffee machine (which was in the description) - but she did not :(. There are a lot of dishes, spoons, folks, glasses, two big knifes, pans, a grater, and something else. If there was a microwave oven - it would be great for us (it is just a wish, it was not in the description, so no claims from us).
Large room (with bed, table and sofa) is really large. It has a huge TV which we did not use :) - we watched everything on our laptop. There are two things to mention: 1) table for laptop is very low and therefore inconvenient. You may use it just for a short time. 2) there is only one window which is located in the corner. Even without curtains it is rather dark in the room (only in the middle of the day when son shines - there is enough light). But if you shut the window with curtains for privacy reasons - you will definitely need a light even during a day. Lamps in the room could be a bit brighter. And, it would be good to have there a chest of drawers because there was not so much places to put our clothes and other things.
Bathroom - is very large, everything is very good. The only small inconvenience that we had was clothes dryer. It was good for small things like t-shorts or socks, but quite small for bed linen. By the way, we had only one set of bed linen (we could buy additional one) and that was rather strange for us - how to live two months and use one set only. We had to be creative to dry it fast after washing.
There is a vacuum cleaner. I wish we had there some rags and detergents - but we had to buy everything ourselves (I don't know if the host expected us to clean the apartment during our staying - but we did clean it for our convenience).
So, again, the apartment is quite good. For a short period (like a week) - it is really very good, but since it is offered for 2 months period - it could be a bit more "home-like" than it is. If we have a chance to come to Berlin next year - we will probably take this one again.