Rankins is a player who draws some mixed reviews. Those who like him, note is raw strength and quickness which allows him to win a lot of battles. Rankins is also a fairly balanced player who is strong versus both the run and the pass (with maybe just a slight edge as a pass rusher).
On the flip side the concern is that Rankins is a little undersized for what some defenses are looking for and he might not easily be able to add weight. The other concern is that his success has been primarily due to his quickness/strength natural abilities and he’s not really developed good pass rush moves and technique. At the NFL level he’ll need to rely on more than just his natural abilities.
While some teams may opt to pass on Rankins, that likely will be a mistake. Rankins may need to work on some additional counter moves and working on his consistency, but shows a lot of natural talent to work with. The fact that he succeeds both versus the run and the pass is a big plus as a lot of players are more of one than the other at this point in their careers. Rankins should be a top 20 pick and an immediate starter.