I would definitely agree that it isn't the best graphic, but I think it does an admirable job of portraying the primary thing it was created to portray (I assume) -- the context of radiation dose levels. I can very quickly eyeball the order of magnitude difference between a plane flight and a chest X-ray, while I could also dial down to the more precise differences if necessary.

The "radiation doses combined" transition seemed fairly clear to me. In every case the collective doses are measured in the new SI-prefixed unit delineated by the scale on the left. If I were to criticize anything I would be a little more wary of the color choices and the box labeling. The = sign and parenthetic dose notation seems a little confused (the blue box dose size uses a different convention from the others).

While the chart could layout some things a little more clearly, I think that Minard's chart shows that one shouldn't reduce information content solely for the sake of simplicity.