I did a google search on "Catastrophic success" and got:
"The plan that Army Gen. Tommy Franks, the commander of U.S. Central Command, came up with stresses adaptability and flexibility. "One of the bookends on this plan was, let's be ready for catastrophic success," Myers said. "The other bookend was this is going to be a long, tough fight. Somewhere on that spectrum is probably where it will settle out."
With Iraqi Regime Going Down the Tubes, Where's Saddam?
Date: Monday, March 31, 2003 @ 9:49 AM PST"
http://www.scienceblog.com/community/article-print-1355.html

Now, as Franks is using the phrase, I imagine he means before the invasion actually begins Saddam just caves, we kill him, or someone takes him out and this results in chaos- due to a power vacuum.
So I would say the actual results was near the "Catastrophic success" side of the "bookends".
Related to [as I recall] this is similar to what a Iraq scholar was discussing quite a while ago [at least 6 month ago], he was discussing how he had talked to miltary about possiblity of Iraq "shattering", and problems relating this. And he had thought that at the time of this discussion that is is what had actually occurred.

I think it's fair to say that the US Military was expecting a tougher fight.
It's just a very bad idea to underestimate the enemy, but also a miltary leader does not want to interfere too much with a successful assault. Generally speaking, a Patton is better than a Montgomery.
And as far as logistic goes a tough fight is quite different then a quick strike into Bagdag- the point of the spear gets very thin.