It has relatively simple rules but very solid strategy (rewards logic and duplicity). The games are short, so you never feel "stuck" on a long game and when you're a beginner, you can rapidly absorb new lessons and strategies and apply them to the next round. The replay value is tremendous.
I have observed/heard about the game not "clicking" for some players the first few times. You _can_ reason out substantial amounts of information by sharing claims and thinking hard about what you personally know, and you _can_ tactically disrupt other people. I think if you have a crowd of new people, it helps to have an experienced player sit out one round and emcee, encouraging certain lines of thought and discouraging others. One of my friends said he only really "got" it after the third round, when he saw me spin a story from start to finish so that I could pin a wolf on someone when I in fact was a wolf.
I also love Dominion, which others have mentioned. (That's my personal favorite; Werewolf is my friend group-favorite.) It is in a very different genre, but it also has fast-cycling games, deep strategy vs. simple rules, and huge replay value, which are three aspects of board games that I really value.