We all have something in our lives that we are sentimental about, and even a glimpse of that object/idea can bring back happy memories. And nostalgia makes the remembrances of those experiences feel better than comparable experiences today.
However, my question is differentiating between the extent of happiness gathered through these different experiences:
Happiness received in those times by those experiences. (Playing Diablo 2 in 2001)
Happiness experiences by remembering those times, today (aka nostalgia) (Reminiscing about Diablo 2 sessions today after seeing some images of Rogue Encampment)
Happiness by doing those same things today. (Playing Diablo 2 today)
Which of these is the strongest and why?