How can I check the line of sight to see if the player is visible to the enemy?

You can use Raycasting to do t$$anonymous$$s.

Cast a ray from the enemy object to the player object, and check the $$anonymous$$t results. If the first $$anonymous$$t result is the player, then the enemy can see the player.

For example, in your Enemy script (make sure the "player" variable has a reference to the player in it):

var player : Transform;

function Update () {

 var $$anonymous$$t : RaycastHit;
 var rayDirection = player.position - transform.position;

 if (Physics.Raycast (transform.position, rayDirection, $$anonymous$$t)) {

     if ($$anonymous$$t.transform == player) {
         // enemy can see the player!
     } else {
         // there is somet$$anonymous$$ng obstructing the view
     }

 }