The most significant change to RIFT's beta is the increase of the level cap -- to 27 -- and the unlocking of the Stonefield and Gloamwood zones. In the prior three events, players were limited to a maximum of level 20 and confined to the two starter areas. This round, players looking for more PvE dungeon goodness should enjoy the Darkening Deeps and Deepstrike Mines, while PvPers will rejoice at the inclusion of Warfronts (Black Garden for level 10 and above, The Codex for level 20 and above). Warfronts are like World of Warcraft's battlegrounds or Warhammer Online's scenarios -- instanced PvP areas where (hopefully) evenly matched teams can go at it under special conditions.
There are several quality-of-life improvements rolled into this patch as well. The skill soft queue has been upgraded to a full next ability queue, more hotbars are available, and many of the souls are getting tweaked. You can read the full patch notes here.