I would describe it as interesting...maybe challenging...but hard?
For me that provides a slightly negative connatation.
I'm not sure how widely that connotation is shared...but even assuming it's universal, does that have to be a bad thing? Put another way, if someone were to describe their experience in training aikido, and they used some adjectives that have negative connotations, would you wonder why they were training?
In Autumn Lightning
, Dave Lowry wrote the following passage. It describes a kind of "hard" that I encounter over and over and over again in the martial arts. I don't expect it to ever go away. If it did, I don't know that I'd continue training.
"There were moments in my training, too many to count, when Sensei's bokken came slashing at me and I thought with the merest periphery of my consciousness about the parry and counter. The center of my attention was taken with my own limitations, and I wondered how much more I could take. From the moment I had stepped into the dojo, I began a struggle with boundaries, imposed by my mind, that threatened and bullied at every step to overwhelm me…I fought a dozen duels with myself for every cut I made with the katana. Sometimes I won, sometimes not. The nights when I won over myself and pushed back the limitations a bit, I would jump down under the stone bridge in the park on my way home, full of confidence and contentment, rubbing my sore muscles briskly, reveling in the whole specialness of being a part of the classical martial arts. But there were other nights, many others, when I crept down under the bridge, tucked my arms around my legs, and stained the knees of my jeans with tears."