Now, I know the title might be misleading, maybe even already discussed, but here is my idea:

Every skill in game mechanics differs in to many different categories, like active/passive, magicka/stamina, class/weapon etc etc. However there is another category that none really thought off, it is of a skill is allowed to crit. The skill affinity of critical potential is mainly affected by one factor: damage/healing input.

What does it mean you say? Well it means that when we do get crits on attack and healing skill we dont get crit on anything else. From all the Active skills there are many that dont crit and when you think about it, they should. Taking shields for instance, any shield in game dont crit, why not ? Maybe it should, like if it crits duration is doubled. How about blocking ? When you crit on blocking the cost of it is reduced. Crafting ???? Ha! Double craft on crit! There are many possibilities, and a chance to put some more life in to this game.

In conclusion, I think every action we take in game should have its own defined crit potential.