I post in the weekly Road Racing and Training Thread. I have used the Hansons plan twice: 1) Targeting a 2:55 marathon at Gettysburg this past spring, 2) Targeting a 1:20 half-marathon at Philly this past September.
I ran 2:55:57 and 1:19:57. It's very simple. If you follow their rules, you should perform on race day.
The problem is, most people either don't follow their rules or have great misconceptions about the program leading to unwarranted criticism.
Run ALL OF THE PACES correctly. Don't run faster than 5k-10k pace for speed intervals, don't run faster than MP-10s for strength intervals, don't run faster than MP for tempo runs, don't run faster than moderate pace (~MP+35-45s) for long runs, and run all of your easy/recovery runs very slowly (1:00-2:00/mi slower than MP).
If you run decent volume (their generic Advanced Plan gets up to ~65mi/week), you will hit your goal time.
You can modify the plan by adding more mileage on easy/recovery days or during warmups/cooldowns, but you shouldn't really modify the amount of quality (with the exception of the long run). I peaked at 75/mi week during my marathon buildup with a longest run of 17mi, and I peaked at 61mi/week with a longest run of 14.5mi.
I am not sure why everyone is so fixated on the 16mi long run when the Hansons clearly state the rule of thumb for long runs is no more than 25% of weekly mileage and no longer than 3 hours. If you run 85/mi week and your long run pace is 7:00/mi, there is nothing wrong with a 20-21mi long run (2:40-:47 time spent running).
The Hansons just don't want 10:00/mi runners or runners peaking at 50mi/week to be running 20mi long runs as that would be disproportionate to the amount of other training required and could very likely lead to injury.
I hope this helps anyone interested in or unsure about the plan. It's not for everyone, but the science behind it has worked twice for me and many times over for friends with whom I train.
Happy running.