Easiest answer would be for the story to be interesting and engaging, I suppose!

Not every adventure is a series of wins. Sometimes bad things happen, one falls out of luck before good fortune arrives. And not every adventure has a happy successful ending either.

But when I think of good stories and adventures after the fact, the ones that were memorable and fun are what come to mind. Both the good moments and the bad moments. If I can remember it fondly and miss those days, it was a good time.

And of course, my usual idea of an adventure is going on an exploration, beating up some bad guys (or trying to, anyway), getting into mischief (or trying to, anyway), and being rewarded for it. Though, sometimes the adventure itself is the real reward.