By accomplishing something means it should be something hard to do? if so, nothing, I don't like things that are hard by their nature in videogames because I don't like wasting time repeating the same over and over, I lose interest as I am not competitive, so I don't feel what you call satisfaction on achieving it. If I were paid for it it would be very different.
If by accomplishing something is a reference of doing something that I wanted to do since long time ago and finally doing it, I could say when I finished Vagrant Story or Athena Awakening from Ordinary Life. Two games I wished for long to play and finish but never found the right moment until not so long ago :)