...
private int _score = 0;               
...
public void CardRevealed(MemoryCard card) {
  if (_firstRevealed == null) {
    _firstRevealed = card;
  } else {
    _secondRevealed = card;
    StartCoroutine(CheckMatch());   
  }
}

private IEnumerator CheckMatch() {
  if (_firstRevealed.id == _secondRevealed.id) {
    _score++;                             
    Debug.Log("Wynik: " + _score);
  }
  else {
    yield return new WaitForSeconds(.5f);
    _firstRevealed.Unreveal();    
    _secondRevealed.Unreveal();
  }
  _firstRevealed = null;           
  _secondRevealed = null;
}
...
