There really isn't anything to add to what so many others have already said about this episode. After so many years of seeing Patrick Stewart as Captain Picard, it is easy to forget what a versatile actor he is. This episode takes him deeper into the character of Picard than almost any other episode, and enables him to experience a "reality" and a depth of emotion that most fans wished for him, but knew he could never have as a Starfleet Captain. You are almost sorry for him when he is returned to the present.
"The Inner Light" is a breathtaking example of the writing and acting that made Next Generation the best of the Star Trek series.