What does it mean that the judge is a keeper?

Answer 1

This is a term derived from fishing. It means that they are "good enough" to keep at whatever they're doing. In the context, it seems to mean that the judge is doing a good job according to whoever made the statement -- this could be a good job being a fair judge, or if the speaker is a criminal, it might mean that the judge is bad at passing judgement and the criminals like him because he lets them off easy.