He now plays with other dogs. I'm so proud of him. First he was afraid and defensive of other dogs, then he was gradually getting calmer around them, then one day he just seemed to turn a corner all of a sudden. He's even learned to play-bow.
Granted, his idea of play is 'running around go crazy mad play', but plenty of dogs like that, especially younger ones. Recall is about 60-70% reliable at the moment so he can only come off the lead in certain places.
Here he is with his big nose that he likes to use as a poking stick.