(a) his style is internally consistent with itself, instead of being a scattering of random mistakes,
(b) while his style is different, he doesn't do anything that majorly impedes readability, and
(c) he uses the style for a particular artistic effect, instead of just using it because he is too lazy to press SHIFT.
http://www.gvsu.edu/english/cummings/caps.htm
(a) his style is internally consistent with itself, instead of being a scattering of random mistakes,
(b) while his style is different, he doesn't do anything that majorly impedes readability, and
(c) he uses the style for a particular artistic effect, instead of just using it because he is too lazy to press SHIFT.