A tactic available in a game which is loved and loathed in equal measure. people who abuse a cheap tactic would call it "effective" as it is available for use in the game. As effective as it may be, abuse of a cheap tactic can detriment skill at a game as cheap tactics do not usually require a great deal of skill to utilise in the first place. People can also become reliant on it to win, further detrimenting skill. Cheap tactics tend to proliferate themselves as people adopt a cheap tactic to counter the same cheap tactic used against them (esp. the combo in Halo 2). The debate about a particular cheap tactic can become never-ending, due to the mixed opinions on the debate of cheapness vs effectiveness.
Counter-Strike -The n00b cannon --Kills with pretty much one hit, even when shot in the toe.
Marvel vs capcom 2: Cable's air hyper viper beam is cheap. Playing well with magneto is not cheap as skill is required to be good with him.
Halo 2: Plasma Pistol battle rifle combo aka "The combo"
The fourth installment in Capcom's "Versus" series.
a revamped version of the old-skool street-fighter style games on speed (and probably acid too).
Easy to play, difficult to master.
Although unbalanced character power-wise and looked down on due to it being a 2D fighting game (with sprite quality and animation largely unchanged throughout the series) this game offers an extreme amount of longevity to those who appreciate the game for what it is.