I skimmed through all the responses and as near as I can tell, not one mention of the Stern "Action Button." Hmmmm, imagine that?
For me, I love a machine that has a drop target that opens up a passageway when down. Whether it be an inline drop or a bank (Devil's Dare, Nine Ball). For my friends one of the most underrated features of a pinball machine they are competing on is ME. But I usually fix that after a few games.