The skill system has changed throughout the entire development of the game. Starting off similar to the tree system in Diablo II, the first change came with no pre-requisites and tiers of skills. This, however, would change again to a more open system where certain skills would just become available to dump skill points into. This would change again to the current system that will be used in release.
Every skill becomes available to the player as they level their character.
All skills become available by level 30.
There are no skill points used in the game. Every skill is given to the player.
A player may chose up to 6 six skills to use at a given time. Left and Right mouse click with 1-4 hotkeys.
The 6 skill choices are broken up into 6 categories. Primary and secondary attack as well as 4 unique to each class.
By selecting "Elective Mode" under options, players may opt out of the controlled skill allotments and choose which ever skills they have available for any key.
Players can swap out any of their skills with a 5 second cool down (in Normal) on that skill unless in a town (no cool down).
On higher difficulties, skills will have a longer cool down for swapping.
Runes are used to augment characters' skills. They will help add diversity to character builds with changes to the skills' mechanics. The system has gone through just as many changes as the skill system. It started off as five types of droppable runes with seven ranks each. This changed to an attuning system where certain runes would attune to a particular spell. However, the finalized version differs greatly from these earlier iterations.
Runes are not dropped but automatically available to each skill.
Different runes will become available to the player as they level up.
Runes will become available at level 6 and will continue to unlock at various levels all the way through level 60.
Each skill has 5 different runes available for it
Each rune augments the original skill changing anything from elemental damage to a complete change in the mechanic such as a single-target into an AoE.
Players may swap out the rune at anytime with a 5 second cool down on the skill affected unless in a town (no cool down).
Harder difficulties will have an increased cool down on rune swaps.