Mythos, the long-in-development mythology-inspired hack-and-slash MMO. As a prelude, HanbitSoft and Frogster have released a massive patch to the game's current open beta client that, among other things, raises the level cap to 50 and introduces a new explorable region called the Umbral Peaks.
Dungeon play has also been optimized for groups according to a Frogster press release, and the client has received a "comprehensive localization update." Finally, lots of new guild-centric features have made it into the current build, chief among them a guild message board, storage safe, and a guild ranking system.
You can download the open beta client for free -- and learn more about the game -- at the official Mythos website.