Since 1947, there have been 130 recipients of Major League Baseball's Rookie of the Year Award. The first winner was arguably the best—Jackie Robinson—so good in fact that the award is now named in his honor.
Winning the ROY Award, of course, is no guarantee of greatness. In some instances, past recipients didn't even have very good years during their ROY seasons...more on that later.
Hellickson, despite a lack of over-powering stuff, has the makings (and makeup) of a front of the rotation starter. Kimbrel, with his blazing fastball that touches triple digits, and a knockout slider/curve, can easily become the premier closer in the National League for many seasons to come.
When it comes to having a successful rookie season, though, there is certainly no guarantee that said player will have a career equaling their first-year accomplishments.
And, of course, you've always got to look out for the dreaded "Sophomore Slump." Here's a look at some of the most profound second-year drop offs in the history of the Rookie of the Year Award
Note: I've excluded players that missed a significant amount of time during their sophomore seasons due to injury.