It's obvious that Pokemon designs got a little more intricate as the generations went on, so I can give a pass to Pokemon like Ditto, Voltorb, Gastly and Grimer as being overly simplistic compared to newer ones. There should be no excuses for newer Pokemon though, which is why I really don't like Roggenrola. It looks like it was created by a kindergartner who just started learning about shapes, drew something, showed it to their parents, and it was turned into a Pokemon.
Heck, as a guy with little to no artistic talent,
I drew this picture of one in 45 seconds or so, and with some shading, it'd look no different than the actual thing.