Are the good deeds he performs after his repentance accepted, or are they from the whispers of Satan, and will he be held accountable for spending a long time playing?

Your good deeds are accepted, God willing, and you will be rewarded for them in the Hereafter. You should have a good opinion of God, continue performing righteous deeds, associate with good people, persist in the remembrance of God, and be keen on earning His pleasure. There is no harm in entertaining oneself with permissible games, provided that it does not consume a lot of time and is limited to what is needed to rest the soul and be active in obedience and study.