I can only share my experience with Viktor, as it was similar to yours.
He didn't know how to "play". I would throw the ball and he would look at me... took him to an off-leash park, when no one else was there, he could free-run a football field, but he would be right next to me.
Slowly, over time, he learned to play ball (sort of) and might wander off on his own a bit.
I think he will never be what some/most people would consider a "normal" dog, but I love him to death and will do only what he feels comfortable with and try to expand his horizons without putting undue pressure on him.
So, I guess my advice is to take it slow and have reasonable expectations.
: 5 year old (DOB: 8/31/2008) GSD rescued 10/15/2011
Everyday, we get closer