This isn't necessarily a thread for posting fixes to DRK, although it does need them. Rather, this is about giving the tanks more flavor via job mechanics.

Currently, the three tanks operate nearly identically when it comes to their "gauges." Build resource, spend resource (Really, all of the jobs suffer from this). This actually suits WAR very well. I'm not certain about PLD, personally.

My proposal: Take a cue from the designs a certain other game has used. Have the DRK bar start off full, replenishing over time or through builder abilities (like the current ones), or even a mixture of both.
"How's this different from mp/mana?" Simple. Have the rate be much quicker, like the energy bars from WoW Rogue or Druid.

I think a change like this would be ideal for DRK because they don't exactly have a ton of different dmg options, but this 'could' allow for those skills to be used more often, acting as an indirect buff to the job as a whole.

TL;DR: The tanks operate way too similarly. Change at least one up a bit. Preferably the one that needs the most help.