I kinda prefer Resistance/Avalon to Mafia/Werewolf. You're making me wonder how well they would work as forum games. Seems like it's too dynamic to work properly, with fairly rapid fire team selections, votes, card uses, etc.
It does some things better. The accusatory dynamic is a lot quicker getting off the ground. Unlike Mafia, which (even in person) takes a while to get the suspicion going. But I think Mafia is a deeper game, overall. Probably because of the community and metagame around it. Avalon/Resistance is super well designed, though. Simple and deep.
But as a forum game? That would be some crazy shit. It's a lot more dynamic and depends on more physical scenarios with all the cards and voting and flipping and such. You don't "publicly" vote or anything, like Mafia. It would get kind of messy as a forum game, IMO. Lots and lots of PMs would be required.
It will be your first time, but once you get the rules under you, you'll be able to bang out a game in about 2-3 hours. Such a great, tense experience.
I bought it completely on a whim based on it's theme. I'm a sucker for the cold war. Only after did I realized it was highly rated.