We've spent 5 nights in Gili's apartment in January (2 people), and it was really good. The apartment is located just outside of center kreuzberg, but is very close to Ubahn, so it's easy to get anywhere quickly. The area is really fine and the apartment is easy to find. Inside there is a small kitchen with all you need. The bedroom is nicely designed and comfortable, nothing was missing. Heating systems are excellent, as well as hot water which are available constently. It's not huge, but for 2 or even 3 it's really an all-you-need comfortable place for winter (and of course all other seasons as well....)
Gili is very nice and is available easily for any need, he has no problem to pop up, and he texted to see that everything was fine, day after we arrived, and before we left.