Elective Mode in Diablo 3 is a design mistake. Further, Blizzard knew it was a design mistake, but they caved in to the whining of the hardcore, and thus weakened the game as a whole.
First, a quick explanation. In D3, you have six categories of abilities. Each category has 3 to 5 abilities within it. For example, the Demon Hunter has Primary Attack, Secondary Attack, Defensive, Hunting, Devices, and Archery categories. Under the default settings, you can only pick one ability per category.
However, if you go into Options, you can turn on a setting called Elective mode. In Elective mode, you are no longer restricted to one ability per category. Instead you can take multiple abilities from the same category, like two Defensive abilities. You are still restricted to 6 abilities in total.
Elective mode is more powerful than the default setup. This is obviously true because all default builds are a subset of elective mode builds.
The reason elective mode is bad is that it destroys any semblance of exclusive choices, which is the major advantage of Blizzard's new series of explicit choices model. Instead, it replicates the worst feature of talent trees. As I wrote about talent trees:
The lack of explicit choices means that all talents within reach are compared to each other and ranked accordingly. And this has lead to some awkwardness. For DPS, damage talents always outweigh survivability talents. For tanks, survivability talents always outweigh damage talents. So for a final build, the only choice is between a few talents that you don't really care about, that aren't really important to your role.
In a talent tree, it is extraordinarily hard to make someone choose between two good choices. Most of the time the player will take both, and drop a third, less important choice.This same pattern occurs in Elective mode. Trying to choose between two good Defensive talents? Don't make the hard choice. Turn on Elective mode and take both.
Restrictions breed creativity. Restrictions make games interesting. If you don't have access to both good Defensive talents, you have to choose one and adjust your play-style to match. You have to get the most value out of a weaker ability in a different category.
However, the hardcore players hate being restricted. They hate having to make choices. All they see is that it lessens their power. Thus they will whine and moan until the game developers give in.
This is one of the most important responsibilities of the game developers. To tell the playerbase that they need to deal with weaknesses, to work around the weaknesses with new tactics. Instead of watering down the game by erasing the restrictions that make the game interesting.
Blizzard knew elective mode was a mistake. It's not the default system in Diablo 3. The option to turn it on is buried in the menus where, realistically, only the hardcore will find it. The default system with the different categories produces far more interesting builds, in spite of--or maybe because of--the fact that default builds are weaker.
Blizzard gave in to the hardcore players who hate restrictions and weakened the game. The default ability system produces far more interesting and varied builds than elective mode. Unfortunately, good elective mode builds are far more effective in practice.