What makes a good pass? 

The weight of the pass. The accuracy.  The intention behind the pass.  Most would answer all of the above.  

But what about a pass to feet?  

I often hear coaches call a pass to feet a "good pass" and a pass not to feet a "bad pass".  I would encourage you to rethink the communication of this idea.  Main reason...its limiting.  To teach a young player that the only "good pass" is a pass to feet you are teaching them a way of playing soccer that limits their play.  A pass into space, a pass to where the player is headed or a pass encouraging the player to move into space are examples of passes that are actually quite good even though they are not to feet.  Limit the "rules" and give players freedom for creativity and  expression on the pitch.