Ruthless

The gem as others have said lacks transparency. Please add an indicator to show when a ruthless blow is ready. This is already done well for fist of war support and I can tell when it is ready by looking at the skill icon. Adding a similar indicator for ruthless would reduce confusion with its interactions by clearly indicating when it is active and making it easy to test and experiment with.

Another gameplay reason for adding indicators is to allow exert builds or similar mechanics that empower attacks to more easily align a ruthless blow and reward the set up. As is you pretty much have to guess when ruthless blow will go off if you don't keep count of every single attack since you entered a zone.

The core of the stun mechanic revolves around three key elements: reducing an enemy's stun threshold, increasing stun duration, and maximizing your single hit damage to trigger a stun.
In theory, both reducing enemy stun threshold and boosting your single hit damage should deliver positive returns for a stun-focused build. This is not the case in practice, however, because a core pillar of nearly all dedicated stun builds is the Ruthless Support gem, which grants a base stun duration of 0.8 seconds on the Ruthless Blow from every 3rd hit.
If your base single hit damage is high enough and you stack excessive enemy stun threshold reduction, you will very likely stun the enemy before your Ruthless Blow lands. Non-Ruthless hits, by contrast, have a default base stun duration of just 0.3 seconds. For a build that also stacks increased stun duration, this means a stun from a Ruthless Blow can reach up to 8 seconds, while a stun triggered by a non-Ruthless hit will only be 3 seconds.
In other words, stacking too much enemy stun threshold reduction and single hit damage can end up penalizing your stun build, rather than enhancing it. For this reason, I would like to propose a balance change: as long as a skill is supported by Ruthless Support, all stuns triggered by that skill should use the 0.8 second base stun duration, instead of limiting this bonus exclusively to the Ruthless Blow on the 3rd hit.