While Oklahoma's Trent Williams is seen by many as the higher upside pick - the reason he went two selections earlier to the Washington Redskins - Okung is a fully developed player who still has some upside, especially since he'll be coached by Alex Gibbs in Seattle. He's not an ideal zone blocker at this point - he tends to get a little wobbly at the second level - but there aren't too many questions about his character, work ethic, and learning ability. Eugene Monroe(notes) and D'Brickashaw Ferguson(notes) are reasonable comparisons.
Here was my Tale of the Tape take on Okung ...
Pros: In pass-blocking, which is Okung's primary strength, he takes a consistent first step and fans out very well against ends trying to get around him. He's got a great kick-slide outside, which he will use to take pass rushers out of the play, and also to create outside rushing lanes. Drive-blocks decently - this is an underrated part of his game, and he's also good at pinching guards inside when asked to do so. Okung is very persistent when he gets his hands engaged - he doesn't take plays off even when the play goes away from him. He chips well when he has to take on double teams; he's very adept at pushing one defender back and engaging another without losing position or leverage. When he backpedals to take a bull rush, he's very good at establishing a foundation from which he can strike out. Nice footwork in short spaces. Not an especially convincing downfield blocker, but he has impressive power when heading up a couple yards and pushing a defender out of the play. Plays with a wide base, which allows him to better counter spin moves and other trickery. Allowed just one sack and two quarterback pressures in the Cowboys' 2009 season. He ended his collegiate career in the Cotton Bowl - his 47th straight start.
Cons: When defenders come inside after he's walled them off outside against the pass, he frequently gets pushed back into the quarterback. Not especially agile on pulls and will whiff in space at times. Footwork is decent for a tackle noted more for agility than power, but he could keep better balance when heading to the second level. This causes him to lose a lot of power on the run. As sure as he is at the line, he plays like he's on a tile floor downfield. More vulnerable to inside moves than outside rushes, but usually has the quickness to recover in time. Did not do shuttles and jumps at the NFL scouting combine due to a groin injury.
Conclusion: He doesn't blow you away with his power, but teams would be hard-pressed to do better than Okung as an immediate pass-protection solution. If he can add in-line power and upfield balance to his toolkit in the NFL, he has Pro Bowl potential. He'll help any team that takes him, and he's got the work ethic to take it all the way.