I am concerned that the year long wait/hype has possibly set expectations too high (absence makes the heart grow fonder). His athleticism and overall talent are obvious but there are parts of his game, not including anything injury related, that have me slightly concerned about playing him at mike linebacker.
First and foremost, he does not shed blocks well. Once a blocker gets their hands on him (even tight ends), he usually stays blocked until the ballcarrier is past him. Something that compounds this problem is that he has a tendency to sit back and read instead of attacking off of the snap. This allows time for blockers to get to him and you see him catching blocks rather than attacking, stacking, and shedding. What is interesting is that when he fires off of the ball at the snap, such as when he blitzes, he shows the ability to attack blockers and make the play at or behind the line of scrimmage (the center from USC can testify to this). When he is kept clean, he chases ballcarriers down and generally makes the tackle.
This brings me to my next point. From the games I watched, I didn't see a linebacker who squares up and explodes through ball carriers when he hits most of the time. He is more of a drag down tackler. Don't get me wrong, he usually gets the guy down when he gets there, but it's not generally the type of bone-jarring hit that stops a runner dead in his tracks (outside of the Texas game where made a few of these types of tackles). I don't think of this as a weakness necessarily, just something that I could see fans complaining about.
Finally, for all of the talent he possesses, he didn't really create many turnovers in college. In his three years at Notre Dame, he had 1 interception, forced 3 fumbles (one per year), and recovered 3 fumbles. I bring this up because the organization placed an emphasis on guys that make plays on the ball this offseason. He did have 10 passes defensed in his career though. This is an area that he may improve on, but it is something to consider.
Overall, I believe Dallas is getting a potentially great linebacker and I'm excited to see him play, but he has some things that he needs to work on (as most do) if he is to reach a level that matches the hype of many Cowboys fans. I have no doubts that teams will have a hard time running outside against he and Lee, but I worry about what might happen if teams try to run right at him up the middle. I believe that he will be very good in coverage right off of the bat (he seems to have excellent zone awareness in particular) and will be a real threat as a blitzer both up the middle and off of the edge. I just caution everyone to give him time to get back into the flow of the game and the time to work on/correct the potential flaws in his game that were present even before the injury.