It's funny, I was thinking about posting about this game today.
I was thinking about how many of us have played all of the classics for years and years, and then one day we learn something new about a game that totally changes the way we play.
As most of us learned how to play these by either experimentation (which quickly lost most of your quarters) or by watching others play (to learn the tricks or objective), if we didn't know about it beforehand, we might never learn about.
Just recently, I discovered that - in Mappy - not only could you open doors without being next to them, but you could also CLOSE normal doors that had already been opened! How many times have I played this game in MAME or multis and not known this? Perhaps the instructions on the original explain this - maybe not - but as I don't recall seeing one in forever, I never knew. My strategy has completely changed with this knowledge, and my scores have gone up accordingly...