The change
To slow down levelling, the newest Forever beta build has reduced the experience from dungeon quests. According to the developers, many testers levelled too quickly. Dungeon quests now reward 50% less bonus experience beyond normal quest values.
Why it is controversial
Experience in dungeons has been controversial in Forever from the start: quests were given much more experience while mobs gave less. Some players worried that the quests would make levelling too fast. Others complained that the lower experience from mobs makes repeat dungeon runs unattractive.
Original report: Wowhead