what Valpollicella said.
it was a sort of holding room for coppers who went before they reached their potential. geeky bloke was the devil and Gene was a sort of guardian angel.
if they messed up again in afterlife (like viv) or chose to go with him (like Shaz, chris and ray nearly did), geeky guy got them (the screams were other souls, down in hell). when they solved the big case, they were granted peace. hence, going to the pub. then, once they went, Gene was "reset". he himself never let go of the policeman he should have become.
I miss it sooooo much. agree with Clara, it'd be great if they did one last series, in the 90's.