Game-play is more important than graphics.
I used to own a Spectravideo console/computer. I played for hours with games which had silly graphics.
It's like asking what's better in a book, the plot or the font. The plot is much more important but if you have a bad font people are less likely to enjoy your book.
A good and solid gameplay is a must. without it no matter how lovely is your graphics people won't recommend it.
In the early days of CD oriented games one could find cool graphics which wee created as games. People did play with these games just to see the cool scenery but this won't stand these days.
Btw, graphics is not the only element. You can easily mention sound and music. If you'll have a great gameplay, cool graphics but bad sound design and awful music people will run away from your game.
Also, as mentioned before, it depends on the game category. In some categories people expect more from the graphics side compared to other categories.
Bottom line, it would be best to focus on gameplay and once you have a solid mechanics invest in graphics and sound and animation and presentation to match the gameplay level.