Elementalist doublecast skills, "a new type of spell that casts on you as well as your target," are part of this update. Several current Ele skills were reworked to fall under the doublecast umbrella. Even more skills got changes to make the Elementalist more versatile in varying situations, adding extra functionality to some and changing how others work entirely.
Finally, hard mode enemies were given a pretty big change: Their armor levels were lowered and their health was raised. Previously, Elementalists were at a bit of a disadvantage in hard mode because the increased AL of all foes meant a big decrease in the amount of damage Elementalists did. This change means that Eles will start seeing much larger damage numbers, making them more of an asset in hard mode.
As with most big Guild Wars updates, this one comes with lots of explanation and commentary from the Live Team. It wraps up with a promise that the devs are not finished with the Ele by a long shot: "In the next few months, we'll evaluate the shifts created in the metagame as a result of these changes and make further adjustments to skills that are not in line with our intentions. Additionally, we'll be working a second update to address issues with some of the Elementalist non-elite skills as the elites in this update settle into their places."