My list of what is important.
1st is gameplay
2nd is techically good graphics, no stuttering, graphics bugs, etc.
3rd is the eye candy, it doesn't matter much if the game itself rocks.
Let's take Morrowind for example. Of course when it was first released it was among the best, but since there's no point in judging in yesterday's standards, it's rather... well, from outdated to ugly, depending whom you ask, nowadays. Though good enough for me, besides, the overall atmosphere and looks are far more important than details.
Left out story and plot since completly storyless games can work well. Halo CE still doesn't have much of a story nor characters but it is fun to play. And then there's a question if a storyless game is a better than one with totally awful one...
Stylised graphics are better than realistic ones. Those last longer. WoW looks nice still. SWTOR will probably look pretty nice 5-6 from now... Halos with their style fare better than some FPS i know the test of time. GalCiv2 is fun, Elemental WILL look nice for years.
Gameplay always over graphics.