I voted for three:
Stronghold Construction: I really like building cities in games and building castles is even more fun.
PVP Warfare/Guilds: I haven't found an RTS that is capable of delivering in this regard and I am curious to see how Reverie handles it. Will guilds be able to zerg smash down individual players? Will there be longstanding conflicts between guilds or will they do a scorched earth thing and form a peace? I won't have a guild going in, but I am certainly not against joining one if it increases the fun and/or survivability.
Other: Persistent Economy. I am wondering what exactly they have planned for this and I will need to do some research to see what information is currently available. Are there going to be markets for trading or is it going to be a player to player transaction a la Bartering.