Tommy -
I think it's #5, the simple joy of hitting a pure shot.
I say "I think" because I haven't hit one yet...but the beauty of the game is that it lets hope spring eternal.
Actually, I may have struck one pure shot in my life, a 4 iron on a Par 3. I've forgotten the other specifics, but the feel of that must be lodged inside someplace, feeding those hopes. (There was also a 3 iron from the fairway once...once.)
Peter
PS - And "simple joy" is about the best thing around, I think - the pearl of great price.