Good graphics do not equal a good game, on the other hand, Bad graphics can[\i] equal a bad game.
Here are some notable cases:
Minecraft: Not very good graphics (blocky, would be a bad pun to use here). Great gameplay. HD texture packs make it much better imo.
Heavy Rain: Good graphics, gameplay is pretty divided on good or not. Never the less, Interesting storytelling, interesting game.
Super Meat Boy: Good graphics, 2D but well done. Excellent gameplay, the only "hard" game i've played often.
LSD Dream emulator: Pretty unknown game, Bad graphics. bad bad bad graphics, not very good programming even, but can be pretty scary at times and certainly makes you think.
There are also dozens of flash games out there which I don't want to list.
I don't think there's much correlation really between good and bad graphics and gameplay. I've never put down a game because of its graphics, but I have due to gameplay.
That's not so say that good graphics aren't important. Sometimes they're integral to gameplay, not sure if that part makes sense or not. Say there is a button on the wall you have to shoot with a bow, with some good graphics, you could probably put a detailed image of a bow there, people will get the hint. bad graphics you might not be able to do that, might have to colour the button yellow, the same as the bow slot. People might not make the connection and therefore gameplay is lost.
In otherwords, who cares? Good gameplay should be a priority but don't let the graphics slip, you'll never have to worry about it. Not to mention the different meanings behind good and bad graphics.