It was expected Miller would be the number one pick but he fell to the Tigers due to signability as well as other reasons. The Tigers were agressive with him and he only pitched 78 innings in the minors in 2007. It wasn't until 2010 that he would pitch that many innings again in the minors.
Andrew always had a great arm with plus velocity especially for a lefty. He had a wipeout slider that he had trouble locating within the zone and didn't have the best control of his fastball. But his development path didn't help improve his weaknesses, it only exposed him to MLB hitters who took advantage of what they saw. It looked like he was a bust. And unfortunately many tried to evaluate why he was viewed so highly - instead of looking at the total failure to develop the prospect.
When Boston acquired him I took note of it. And when the mentioned how good his stuff still was and their intentions to be patient with him I started to follow him very closely. His spring training showed what he was capable of. And his first couple of starts showed the good K rates, low hits, and good control. But his control reverted to the Miller of old frequently going only 4 or 5 innings with around 4 walks per.
Eventually Andrew took a huge step forward. He asked for help. The pitching coach gave him a tip that Buchholz uses. He does extra warming up before the game and goes at it much harder simulating an inning. The next three starts for Miller featured he same strong strikeout rate and low hits. All this while allowing only two walks total in these three innings.
The reason I think this lesson will stick is something many never knew about Miller. His control issues were mostly to do with the start of the game and settling in. He now has a mechanism to combat this. At 26 years of age and with his talent I don't see why he can't have a very strong career.
I think the biggest thing to take from this, other than the enjoyment of watching a success story, is how much we neglect the development process of prospect evaluation.