As far as his career goes, it was tremendous. He made some mistakes along the way but rose very high. His over-training was a problem at least since entering Stanford and maybe even in high school when he was hammering ten milers downhill in incredible times--obviously, not ideal for training for 5k xc.
He talked about how when he got to Stanford, he was going all out all the time instead of taking easy days and running workouts as workouts. He ran his best toward the end when he was training more wisely. At that point, he ran 13:16, debuted at half marathon in 59:43, ran the marathon in 2:08 in London in 2007, before taking it down to 2:06:17 there in 2008. In all, he ran at least 8 sub 2:10 marathons, which is probably third all time (Khalid Khannouchi has 9 at 2:08:44 or faster; Meb has 9, plus 2:10:03, but the fastest is only 2:08:37, so Hall's average is much faster). But what he also changed, in addition to overtraining, as he started to struggle more, was to stop doing faster pace work. He was running long marathon pace tempos but he stopped doing 10k or faster work, and that to me was key to his falling so far off his best after that, with the one exception of the wind-aided Boston time. I am not the only one to have posted about this over the years, and in fact, Hall himself agreed with us--on numerous occasions TALKING about needing to get back to the track and faster workouts but never following through.