How to make physics collisions act like in old games (NES, SNES especially)

When an Object collides try setting it's velocity to 0?

So:

  void OnCollisionEnter(Collision coll)
     {
     if(!coll.gameObject.CompareTag("isGround")) //To be sure we're hitting an obsticle
     {
     GetComponent<Rigidbody>().velocity = 0.0f; //Stop moving
     coll.gameObject.GetComponent<Rigidbody>().velocity = 0.0f; //Stop other Object
     }
     }

Replace the tag function with your preferred method of detecting the ground. If you don't already have a cached Rigidbody referencing the current one then use GetComponent.

Hope this was helpful.