Episode 2 brings major changes to the game including a new leveling system, itemization changes, and new quests. Webzen's press release states that the revamp should "please various gamers with its simple yet strategic gameplay."
In addition to the leveling adjustments, Episode 2 introduces the custom passives system whereby players may tweak their avatars' abilities via customizable buffs. The mechanic is intended to encourage grouping between new and old players, and the resultant buffs will stay active as long as the party remains intact. Head to the official Soul of the Ultimate Nation website for more info.