Good graphics = functional (conveys information in an easy way, readable fonts, etc) + consistent + appealing.

In a perfect world, we would have all 3 components, but it seems not all are absolutely needed or at least not in all cases. I can imagine a functional and consitent yet unappealing graphics that beat up appealing one that is inconsistent (photorealistic + cartoony and all done by various artist in various styles) and unfunctional (can't really see what's going on on the screen. I would also say these go in that order (the player needs a functional gfx, without this nothing matters, then consistency, and then only if all previous 2 are sufficient the appealingness of gorgeous pictures is taken into account). Sort of like Maslov's pyramid of needs But the trick is, everyone expects gfx to be decently functional and consistent, therefore only appealing part is taken into account in usual cases (unless the devs messed up a big time with their choice of gfx). Also, the appealing part is the only one that is really expensive (making simple consistent and functional gfx is cheap and easy). Also, sometimes devs make a mistake and put too much on the appealing part which turns the gfx into unfunctional (that's the case when we see a "good graphics" game yet we find it unpleasant/inferior to simplier gfx games).