/**
 * Implements hook_comment_insert().
 */
function mymodule_comment_insert($comment) {
  if ($comment->uid != 1) {
    drupal_mail('mymodule', 'notify_of_new_comment', 'admin_mail@gmail.com', language_default(), $comment);
  }
}
 
/**
 * Implements hook_mail().
 */
function mymodule_mail($key, &$message, $params) {
  if ($key == 'notify_of_new_comment') {
    $node = node_load($params->nid);
    $body = $params->name . ' оставил комментарий в теме "' . $node->title . '":' . "\n\n";
    $body .= trim($params->comment_body['und'][0]['value']) . "\n\n";
    $body .= url('node/' . $params->nid, array('absolute' => true));
    $message['subject'] = 'Уведомление о новом комментарии';
    $message['body'][] = $body;
  }
}

Drupal 7