I'm eight hours in and I've just been exploring every nook and cranny of Prague. Did the intro mission, woke up in Prague and it's just been hour upon hour of glorious, wonderful sidequesting; this place is tunnels on air ducts on sewers and everything is connected. I can't walk for ten seconds without seeing something that needs hacking, which leads me on a little mini-adventure seeing where it leads.
I found the Australian SAS dude's apartment, and stumbled upon his hidden safe room, stole all his stuff, sold it to the nearby weapons dealer, then found a back-entrance into the weapons dealer's private stash and sold all his stuff back to him. I'm making a killing here
Haha, I just did this exact same thing! Got access to a storage locker, which i then punched a whole through to gain access to the room next door. I'm looking around, find a secret entrance which leads you into the store! When i popped the secret entrance open, I was thinking "Woaah, now where does this lead!". I love that it all started by gaining access to a random apartment. Fantastic game so far, really enjoying it (minus the lip/voice syncing issues with cut scenes and the background music stopping and starting).