Is Avalon worth getting if I already own The Resistance
There are several new mechanics brought in the game with Avalon. The major ones play around two new characters Merlin and The Assassin. Merlin allows the good side to have some knowledge of who is good/evil but on the flip side The Assassin allows for the evil side to turn a loss into a victory by figuring out who is Merlin. In addition to those two there are some characters that add some other flair into the game such as a good character who knows who Merlin is with the flip side of an evil character to pretends to be Merlin and a evil character who is unknown to the rest of his team. There are some other characters that where kick starter specific and not sure if you can still get them or not but are worth getting.

Overall I think the changes to Avalon add a lot to the game and make it a little more interesting then the basic game of resistance.