Bug fixes and tweaks are part and parcel of every patch major or minor for a live MMOG, but patch 1.5.1 is looking to address one of the hot button complaints about the game: the grind.
To that end, 1.5.1 is aggressively tackling the issue with boosts in XP rates for quests, combat, and even crafting, as well as a reduction in XP penalty for groups. New repeatable quests have also been added. NCsoft is looking to make the game a bit more rewarding as well, as 1.5.1 also sees a significant boost in drop rates for instance bosses.
For more details on the patch read the full patch notes here.