Has anyone written a definitive account of the intelligence failure here? A step-by-step kind of thing, not a pointless "BuSh LiEd!!!" kind of thing?

Yes. A commission appointed by Bush took a look at the nation's intelligence community after the Iraq failure and found it to be severely lacking.

http://articles.cnn.com/2005-03-31/politics/intel.report_1_m...

Thank you, that lead me to the actual report here- http://govinfo.library.unt.edu/wmd/report/index.html