I think the most important thing about graphics is how they impact playability. It's been touched on a bit but to be more precise, if the graphics distract from the fun to be had, then they are bad. This of course is different for every person.
They same issues have been documented in the design of pretty much everything.in website for example, if the page is designed poorly the readers are less interested in what it has to say. Worst case scenario the page is so bad users won't read it at all unless they absolutely want to know what it has to say.
Same can be said for games, unless someone really loves the game, bad visuals can ruin it.