It's critical that the controls be usable and responsive. Graphics aren't so important, as long as they're viewable. You can think of graphics as being comprised of two parts - (a) quality and (b) style. The latter includes, for example, whether the game is designed to look realistic or cartoonish. I'm tempted into realism, but just as over-saturated colours aren't realistic, neither are
under-saturated colours. But good luck getting it right in a world in which modern displays are usually over-saturated on purpose
.
As for the plot...it's nice if it isn't the same old story for every game in the series. I've got to admit, it would be amusing to twist things up by, for example, requiring a certain character widely known for smashing pots like nobody's business to handle something expensive, fragile, and difficult to replace (as in, you have to do more than just buy a new one) to finish the game.