There are reasons why teams have been moving away from taking RBs in the first round. Basically, unless they appear to have epic skills to non-fanboys, it's better to fill other positions. Otherwise, there is a high bust rate, and a short career for most of the others. You need RBs, but most teams are better off waiting until later to grab one.
Gurley looked like a future star, but had the injury - a serious concern. Things have worked out as well so far as the Rams could realistically have hoped - but the reason they gambled on taking him in the first is that if he worked out, they knew he would be a major star. Gordon looked like somebody who if he worked out he might get yards in the right situation, maybe a few more yards than most RBs could.