Put this on your object:

// C#
using System;
using UnityEngine;

public class LookAtTarget : MonoBehaviour
{
     public Transform target;

     void Update()
     {
          if(target != null)
          {
               transform.LookAt(target);
          }
     }
}

Hi! I´m new in the forum. You can try with this...If you are in a 2D Game and your player only moves f.e. in x axys and the enemy is stopped it only will face up the face lloking the player. I add a damp variable so make the rotation softer. I hope you can use it!!

// Script to look at camera

var targetPosition :Transform; // we have to add in the Inspector our target
var damp: int = 5; // we can change the slerp velocity here

function Update ()
{
    if ( targetPosition ) // we get sure the target is here
    {
       var rotationAngle = Quaternion.LookRotation ( targetPosition.position - transform.position); // we get the angle has to be rotated
       transform.rotation = Quaternion.Slerp ( transform.rotation, rotationAngle, Time.deltaTime * damp); // we rotate the rotationAngle 
    }
}