Our old buddy Justin (does he still post here?) had this article from the Hardball Times:
Minor league run environments vary substantially from league to league. As a result, any time we evaluate a minor leaguer's hitting or pitching stats, we need to consider the context of those performances. Alex Pedicini had a brief but nice series at Hardball Times breaking down these league differences, but I wanted to take a deeper look at run environments, including an investigation of how they would model using Base Runs.
More on Base Runs later. Let's start with a graph looking at how the run environments of the minor leagues (and major leagues) vary:
You can read more at the link above, but the chart shows a lot.
The biggest thing that jumped out to me is that the Reds up until this year, have played in 5 of the 7 most run depressing leagues in the minor leagues.