@ Ashida - well, I am not a painter per se, so I reckon the sumi-e could seem more challenging, but since calligraphy is an extremely vast subject, and in my opinion requiring way more complex knowledge than painting, so I would say calligraphy is a real challenge.
The rules of painting and sumi-e are quite similar though (technically), and these are : single strokes, sharing emotions through abstract concept, use of Indian ink.
Calligraphy however has very strict rules, and even the most random looking works need to obey them. Learning how to, means a lifetime.
@RealJames
Not recently. I am preparing 200+ illustrations for my book about calligraphy, thus I need concentrate on 1-2 character calligraphy. I am planning to start learning copying sutras, which usually are 200-300 long.
Of course, anytime I study 臨書 (rinsho, i.e. copying masterpieces), which takes place every day, I create long and wordy works, in a sense. Rinsho is bread an butter of any calligrapher who is serious about this art. But I do it on a practice paper, and these are not to look at but to learn from. It does not mean however that rinsho cannot become a work of art. In fact it is very difficult to capture the spirit, vigor and energy of the old masterpieces.