I don't care if you want to read a wall of text or not, there are still variables that can define a bad game from a good game. These include things such as:

Poorly executed plot that is either completely nonsensical, utterly cliche, just plain stupid, or a combination thereof.

Bad controls or play style. The hit detection is bad, the controls are unresponsive, the way the game is played is just plain stupid, etc.

These are two major points of a game that can factor into it being a bad game. Others can include hideously subpar graphics (for the time in which the game was made), terrible sound, poor mood setting, etc. etc. Usually it is a combination of these that constitutes a bad game.

To determine whether a game is or is not bad, you simply take the following factors.

Every variable that is, in fact, bad (I can prove these on a case-by-case basis). What the game is intended to do. For example, a game with a poor story that is mainly made to be a mindless shooting game can still be a good game. A game that is supposed to be a mindless shooting game with few weapon choices, bad hit detection, and wierd controls, however, is another case entirely.

Once the variables have been properly assessed, it is a simple matter to determine whether the game is, indeed, bad. One can also do this by looking at the reaction of gamers to the game. While there could be a percentage of gamers who enjoy the game, if the game is regarded as a bad game by a good percentage of gamers who gravitate towards several different styles (for example, if the FPS crowd dislikes an RPG it might not be a big thing, but if the RPG crowd dislikes it, it is another matter entirely), it is generally easily considered to be a bad game, especially after the variables and reasons as to why it is a bad game are brought into light.

Consequently, this is the basic outline of how most game review magazines and other such mediums judge games, and when done correctly it is VERY accurate.