Great gameplay + Bad graphics >> Bad gameplay + Great graphics
Great gameplay + Great graphics is IMO >> Great gameplay + Bad graphics
In addition things like game complexity, presentation, off-line / online functionality (online leaderboards, co-op, multiplayer, trophies, etc), story telling and audio also matter. How much the different aspects matter depends on type of game.
A Pacman game is a less demanding game gerne, but still I much prefer Edgar M Vigdal's Deluxe Pacman (on Amiga and PC, shareware) better than emulating the original arcade game, with its much improved graphics in addition to the many newly added game ideas. IMO Pacman on the Atari 2600 sucks... (nomatter how well the game sold for its time!)
Atari 2600 Pacman:
http://www.youtube.com/watch?v=6paQTUtV89g
