What do you think about/understand about climate sensitivity?

Yes, my understanding is that climate sensitivity is the global temperature response to a given energy imbalance. Basically the same as the definition you gave. I think it's a perfectly reasonable measure. We want to know how the global temperature and climate will respond to a given radiative forcing from our increase in atmospheric CO2.

The average value for climate sensitivity in the scientific literature appears to be 3°C for a doubling of CO2 in the medium-term. Some studies have concluded that if the concentration remains doubled permanently, the long-term sensitivity could be 6°C.

I've always liked Lord Christopher Monckton's climate assessment (see source).

It is centered on the IPCC estimate for climate sensitivity. Most of you probably can't get through the math, I know I could only grasp part of it. So you're best bet might be to head to the Discussion and Conclusions (the first para of the conclusion is particularly telling).

The sad part is, there are believers around here who keep bringing up "the science" and they are going to not only not understand what was calculated, but they are going to ad hominem the author and pooh-pooh this piece as not being "peer-reviewed" as if that alone makes it all wrong..

Yes the definition makes sense. No I don't think it's sensible, estimated values vary greatly and new studies are showing further uncertainty of the effects of feedbacks.

Why bother trying to predict a poorly understood system.

"What do you think about/understand about climate sensitivity?"

Nowt, and niether does anyone else.