Almost everything. Hotel's location is superb. Two U-bahn stations riding you to city center in 20 minutes, trams, buses.
Situated between Mitte and Wedding districts, hotel is only 6 km away from Tegel airport, and 6 km away from Berlin Zoo, and 6 km away from Reichstag, and 6 km away from Alexanderplatz and TV tower. If you're young and on budget, you may save A LOT by walking on foot, otherwise widely spread public transport is at your service.
Staff is highly competent, reception was super-friendly and helpful, cleaning ladies did their job EVERY day being friendly too.
I'd like to stress you can't find a breakfast in Berlin cheaper and better than at Smarthotel - for 5.90 Euro you get unlimited food&drinks (while the range of products was not that wide, it was enough for sure). I'd recommend using breakfast services here for all guests.
Also, the room itself was at the highest level possible for this type of hotel. Large room and bathroom, mini-kitchen with European-made equipment, wide and comfortable bed, adjustable heating, lots of lights - I was amazed by room services and equipment. The hotel building is freshly build and designed specially for its purpose.
I hope my review shall convince Berlin visitors to use Smarthostel services, as well as if I ever return to this beautiful city, no doubt I'll use this hotel again. Thanks!
The only thing bothered me was Wi-Fi which fell down few times for the whole night, especially when it was extremely necessary to make a Viber/Skype call to family abroad.
However, asking staff at the reception to restart routers helped every time.
I hope personnel shall keep a close eye on this issue in future!