The following is a very quick summary. See the Leap Attack rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
Once the player activates the skill, the Barbarian will leap from his current location, to the location of the mouse cursor, damaging and knocking enemies back upon landing. This skill is best used to reach ranged monsters, who are behind enemy lines and to escape tight situations, if such occur.
Leap Attack has not changed much from D2, and has been demonstrated repeatedly in the gameplay movies. The main difference with the D3 version of this skill is that minor damage is dealt to everything nearby when the Barbarian lands, rather than major damage to one particular monster.
At BlizzCon 2010, with just one point in it the Barbarian could leap all the way to the visible edge of the screen, over any number of enemies, and at a very high speed. Flux enjoyed using it in the Battle Arena:
I loved it in the Arena, even though I seldom hit with it, just since the visual is great. The 3D works nicely with it, since your perspective lurches upwards when the Barb jumps, and you feel like you’re flying for a second. There’s a great grunting “RAHHH!” sound too, and you must want to knock something in half with a massive club when you trigger this skill. Ideally that Wizard whose been sniping you with that damn Disintegrate from the far edge of the screen for the entire round. “Hold still and die, maggot!”
Skill tiers were removed for the July 2011 Press Event, and Leap Attack became a level 6 skill. The skill system was once again overhauled for the Beta Patch 13, and Leap Attack was classified as a Tactics skill and moved to level 9. For the Beta Patch 14 in March 2012, Leap Attack was renamed Leap.
Leap Attack seems to combine Leap and Leap Attack from Diablo II, whilst requiring Fury to use. The main difference with the D3 version of this skill is that minor damage is dealt to everything nearby when the Barbarian lands, rather than major damage to one particular monster.