I think O'Brien's done a pretty good job, but he's made a few bad decisions which is typical of any person's first time being a big boss. I think it's interesting that NFL teams are falling over themselves to get him - they probably though the sanctions had a more immediate impact on the program than they really did (the devastation is keyed to future years) and so his 15 wins probably count for a little bit more than they should, but all in all, I'd say he deserves a crack at the NFL (anybody that can turn McGloin into an NFL starter in one year has skillz).
I don't particularly mind O'Brien going to the NFL - even after two years. He stabilized the program at a particularly difficult time (which really has little to do with his ability to manage an NFL team, which I'm sure some of you will assert as an answer to my first paragraph). Penn Staters owe O'Brien a great deal for his decision to jump on board a ship which could very well have wound up like the Titanic.
What I do mind is that two weeks prior to O'Brien leaving, he apparently forced Charlie Fisher and Ron Vanderlinden out of their jobs. Notwithstanding that Vanderlinden has 8 linebackers in the NFL (which is more than any other position coach) or Fisher's respective successes, I think it's incredibly poor form to force two guys out right before you step away. Let the next coach make those decisions. What was the point in dismissing them when he did?
One last point - I see Penn State is desperate to get Greg Schiano. I was impressed by Schiano at Rutgers. I'm not sure why we're scrambling to grab him after he's just been shown the door after an unimpressive stint in the NFL, albeit at the Bucs. I think they should've tried to get a guy like James Franklin at Vandy (who has Pennsylvania ties, by the way) or Jim Mora instead of getting somebody whose most recent resume line was a failure.
Despite these consternations, there is one bright side - John Butler probably won't be DC next year.
Have a happy new year!