Until recently I used to live one stop from Gesundbrunnen, but I've not been up there recently so I'm not sure how the new building work is coming along. Where the new building is being built used to be pretty much an open space with only a small booking office and a couple of small retail units and snack bars at one side.
There is no good reason the escalators don't come up into the new building. They come up right outside but most people using them will be heading straight into the big shopping centre right next door.
The new building is a fair size and it seems fat too big for just a booking office and travel centre, however that said Gesundbrunnen itself is quite a busy station/interchange.
With the S-Bahn, the busy ring bahn (S41/S42) runs east/west and then there are also three lines that run north/south (S1,S2,S25)
From the S-Bahn platforms you can walk down to the U-Bahn platforms (U8)
There are some local DMU local services that run out into the sticks on non-electrified lines and other EMU (442's) local services including an Airport Express service direct to Schönefeld Airport.
There are loco hauled regional trains and longer distance (ICE) services that stop at Gesundbrunnen just before/after calling at the lower platforms at Hauptbahnhof.
Finally there is quite a bit of freight that runs through the station.
