We'd expect a level 80 skill to be a staple or a big exciting ability to use, but yet Improvisation is extremely underwhelming.
It's extremely situational. I've been playing just DNC ever since the expansion launched and could find just 1 moment where there's nothing going on for a long period of time (and yet people didn't stack for it)... If you use it otherwise, let's say, to get enough esprit for a TS burst, it's still bad because the esprit gain is so low if people are not together.
The only actual (and marginal) use for this ability that I can see, is after a big aoe, to help the healers to everyone off with the +10% increased healing.But hey, so much for a level 80 ability, right?
The only suggestions I can think right now is to add a damage component while the skill is being performed, so it could be worth to use outside of the (very rare) idling phases, or just fill the Esprit bar in a fixed, fast pace and allow Saber Dance to be cast while you're Improvising... Or heck, even rework the skill completely.