Graphics is vital to get gamers to try your game, once they try it, then gameplay will be more important.
Same as real life I reckon! You need to look good & dress well to attract others (graphics), then once they talk and spend time together, they get to know you better and can appreciate your personality (gameplay).
But good graphics vary a lot, its all down to aesthetics. Lots of simple shape games look great (Thomas Was Alone looks amazing in motion).