As it stands, Riddle of Earth is lacking but has great potential for improvement.
This is the current tooltip for Riddle of Earth:

As it stands, Riddle of Earth is lacking but has great potential for improvement.
This is the current tooltip for Riddle of Earth:

Grants Fists of Earth. Also grants Earth's Reply if damage is taken while active.
Duration: 30s
Earth's Reply Bonus: Reduces damage taken by 10%
Duration: 30s
Additional Effect: Extends Greased Lightning duration to maximum
Both Riddle of Earth and Earth's Reply are canceled if Fists of Earth ends.

The GL refresh affect only affects the duration, meaning it will not give you stacks. So if you have 0 GL stacks the effect is meaningless, and if you have 1-2 stacks you will not get GL3.

I propose the change be made so that Riddle of Earth actually GIVES 3 Greased Lightning stacks on activation. This could possibly make it overpowered but would greatly boost its usefulness. Making solo content a lot easier for monk not having to build stacks on a mob out in the field. And making phase transitions and boss jumps (which is its intended use I'm guessing) a lot more prevalent. Or at the very least, give one stack if no stacks are there, even that much would be welcome.