The Resistance is a Mafia/Werewolf variant. If you're not familiar with that game, it's a party game of asymmetric information. Using the werewolf metaphor, slightly less than half the players are werewolves, and the majority are villagers; werewolves know who the other werewolves are, but villagers don't. Each "night," villagers close their eyes, werewolves open them and silently agree on what villager to kill; they close their eyes again, the gamemaster announces that it's "day," and says which villager died in the night. The villagers then vote on whom to lynch. If the last person alive is a werewolf, the werewolves win, and if all werewolves are killed, the villagers win.
In The Resistance, "Imperial spies" know each other, but other players (Rebels) don't know who the spies are. You create a set of "plans," one or two fewer than the number of Resistance players; each set consists of one red and one black card, placed face down and shuffled so that no one knows which card is which color. One player is chosen as Resistance Leader; he proposes an allocation of plans, that is, what players should receive a set of plans this round. Players vote on the allocation, and if defeated, the Leadership passes to the next player to propose an allocation. Once an allocation is determined, players receive plans, and each player plays one card -- either red or black -- face-down to the action pile. The action pile is shuffled, then turned over. If all cards are red, the "plans worked," but if any single one is black, the "plans were foiled" by the Empire. Each side has "three bases;" in the first case, the Empire loses a base, and in the latter, the Resistance does. Lose all three, and your side loses.
Resistance players must always play the red card, while Imperial players have a choice.
Thus, if there are, say, four plans, and one black card comes up, you know at least one of the four players who received cards is a spy. Nobody dies or is eliminated, but over time the Resistance has increasing information on which to judge the trustworthiness of the players. To counteract this, the number of plans is increased at times.
This is, in a way, a definite improvement on the gameplay of Mafia/Werewolf; the basic problem with that game is that the villagers never have any real information to base a judgment on, and consequently the decision about whom to lynch is based pretty much on gut instinct and the feeling that perhaps someone proposing another for lynching is being smarmy and probably therefore a werewolf himself. That's interesting, in that it's a use of interpersonal dynamics as a gameplay element, something not common in games, but the perfect information available to the werewolves means that the villagers have to make only one (or in larger games, two) incorrect decisions in order to lose.
A second arguable flaw is that the "death" dynamic eliminates players; while they can observe the rest of the game if they wish, it's less fun to do that than to play, of course.
The Resistance's "plans" scheme is a definite improvement to the game, since it provides slightly more information to the villagers/Resistance, and therefore a mechanism for influencing perceptions of trustworthiness; and the fact that players are not eliminated is a positive as well.
The drawback, of course, is an added level of complexity; and while the game's complexity is still modest, complexity is never desirable in party games, where the rules must be quickly explained, and where half the players may be drunk.
Still, it's an interesting variant on a proven model.