In terms of worried, Lawrence tops my list. I honestly feel based on the footage I was able to see and the scouting reports I have read, that Lawrence was reach-by-necessity. The top tier guys were off the board and the Cowboys really needed to inject youth into the line. But here's hoping you and the Cowboys see something I don't or can't.
There are quite a few people who are unconvinced that Lawrence will be good, and I think that is because he didn't run a blazing time in his 40 like Barr or Clowney did (although he did run much better at his pro day). However, there is so much that goes into making a good pass rusher and only a small portion of that has to do with a players 40 time.
There are examples of DE's who ran a bad to horrible 40 time and were actually very good pass rushers. Terrell Suggs is one that immediately comes to mind. Michael Strahan and Greg Ellis are a couple of others off the top of my head. Quickness, anticipation, smarts, strength, an understanding of leverage... these are all things that are just as important for a DE as pure straight line speed is.
xwalker mentioned Lawrence's technique, arm length, and his strong hands, and he is exactly right. Those things will help him in the fighting that goes on along the line of scrimmage. Attitude is huge for a DE, and it is something that I've always griped about with Ware. Lawrence plays with an edge and has a nasty streak. That too will help a lot.
Also, while he didn't run as fast as Clowney and Barr... he doesn't take a backseat in the athleticism dept. Lawrence is extremely athletic, with terrific body control, balance and really quick hands and feet. Again, those things mean more than a fast 40 time. He also plays with good leverage, which really, is something you either do naturally or you don't. Coaches can try to teach that, and they can to an extent, but really, either it comes natural or it doesn't.
I have always looked at playing DE and getting after the QB as something that is somewhat of a knack. Some people are good at it and most aren't. Lawrence walked in and made an impact at DE right away at Boise State. His natural ability to rush the QB was on display from the very start of his career there. What Marinelli saw in Lawrence I think, is a guy who is a natural pass rusher. Someone who just knows how to get to the QB, and has plenty of athletic ability to do it at the NFL level. He saw a guy who uses his long arms, big strong hands, terrific athleticism, and a relentless nature to make plays in the backfield, and he was pretty desperate to get a guy like that on his DL.
Here is what NFL.com says about Lawrence:
"Highly athletic. Fluid, flexible and rangy. Terrific balance and body control. Has quick, coordinated hands and feet to slingshot off blocks. Has natural pass-rush ability -- shows burst, bend and closing speed to hunt down quarterbacks. Dips inside suddenly. Terrific knee and ankle flexion -- flattens efficiently and redirects and accelerates smoothly. Explosive tackler. Made an instant impact at BSU and was productive behind the line of scrimmage -- 34 TFL and 20 sacks from 2012-13. Carries a swagger and plays with attitude."
What you notice about that is a lot of what xwalker and myself have been saying about him: Highly athletic, fluid, flexible and rangy. He is a terrific athlete despite not having a rare 40 time. They talk about his coordinated hands and feet, and that is vital to a great pass rusher. They talk about his knee and ankle bend and how smoothly he plays.
As for his negatives, there aren't a whole lot and those that are there either won't matter that much in Marinelli's defense (a tad undersized for DE), don't matter because he isn't an OLB (isn't used to playing coverage), or isn't a negative to me (plays with an attitude).
This is too long, so I will just say that I think a whole lot of fans are underestimating Lawrence's athletic ability, his natural pass rush ability, his lateral agility and the strength in his hands.
Also, not many are talking about the edge he plays with and what it can do not only for his game... but for the entire DL. That should not be overlooked. It is something we've been needing in Dallas for a long time, and Lawrence has it in spades.
You should start getting excited about Lawrence and what he brings to Marinelli's line. They didn't have him ranked the 20th best player in this deep draft for nothing.