Of course terrible graphics could make a game less enjoyable BUT gameplay is really the most important thing! You can't go about saying that just because one megaman game had better graphics that it would be better then another, or that one Mario game had better sky textures that the original is plain bad. Its unreasonable to say a games poor graphics would make it bad. Gameplay is what makes a game enjoyable, and all games are supposed to do is have you enjoy them.
While gameplay is more important since it's obviously a game, graphics allow for better gameplay and story. I don't think Uncharted would have been possible on PS1. I don't think it would have had the same impact with PS1 graphics, no matter how great the story was. Also, the gameplay wouldn't have been possible either. The same goes for a lot of games. With PS4 and next Xbox we will surely see more new ideas that will come in consequence of the better graphics. It's the sum of all parts, and it all depends on what developers want to focus on.
If you only play games that are graphically advanced, then you have missed out on some great classics. Super Mario Bros, Sonic the Hedgehog, Legend of Zelda, Pac-Man, GTA San Andreas, and Super Mario 64 are all innovative games that feature iconic gameplay. None of these games have good graphics by modern standards. A game could be made that features amazing, lifelike graphics that is about watching paint dry. Still, that game would be boring because it lacks good gameplay.