If you want a nice listing of the "mistakes" of this war in Iraq, here they are, nicely spelled out by (retired) General Anthony Zinni, the special envoy to the Middle East who resigned over the issue of the invasion.
Mistakes implies that there might have been reason to invade Iraq if containment or diplomacy didn't work. But, work for what? I think we have to back up further to look at our relationship with the Middle East. General Zinni lists that as the second mistake. I'd make it the first. And after that, the war has no justification, so arguing strategic or tactical mistakes is an academic exercise and takes the focus off the underlying issue.
But, for those of you who are arguing how things were bungled, check in with the General.
....hey, do what you want....you will anyway.