I don't think Rumsfeld should resign (unless possibly he is replaced by Tommy Franks), but IMHO we should have done a better job anticipating that post-invasion Iraq would be chaotic, and dangerous, and we should have planned up front to have the troops and the equipment in place as soon as possible. We showed after Pearl Harbor that the U.S. was capable of rapidly building up both men and machinery to meet the task at hand. In this case, it appears that we're lagging in supplying of necessary materials, and we're scrounging for troops (even sending OpFor from Fort Irwin which is astounding).
We should have been planning to expand the size of our armed forces two-years ago to not only recover from the Clinton years, but to support a long-term committment to Iraq, it doesn't seem as that has been done.
So in that respect, the criticism of Rumsfeld is far. However, I don't know if anyone would have done better, and there are far more areas where Rumsfeld has done a tremendous job, force re-alignment for one. The efforts to get him removed IMHO are nothing more than grandstand by a group of pols who smell blood in the water.