Grz and McAvoy have had great chemistry playing together since their college days. We'll see if Grz can handle the increased workload, but from an on-ice talent, a Grz--McAvoy pairing should be pretty effective. I worry about Grz's size being a potential red flag in the playoffs with the increased time and physical attention he'll get in a playoff series, but we'll cross that bridge when we get to it.
Carlo will be the anchor of that 2nd line and by all metrics, he's been an excellent top 4 defensive dman and one of the best in the league. The last couple of years, he's had to cover for Krug's tendency to be a bit loose on D, so getting another partner who is the anti-Krug in Lauzon ( size, physicality, defensively aware but lacking in offensive gifts ) will be interesting. Lauzon -- Carlo on paper has the potential of being a very good 2nd pairing shutdown tandem.
Kevan Miller is back but it's unknown how good he'll be. Zboril just signed a one way deal, so they are fully prepared for him to come in and take a roster spot. Clifton has guts and game, but has a tendency to be too much of a cowboy ( Cassidy's endearing term for it was Cliffy Hockey ) at times so he definitely needs to be sheltered. John Moore is an effective NHL quality depth veteran coming off the bench.
There's a lot of question marks but the potential is there to be something pretty good. We hear rumors of the Bruins shopping for a top 4 LD to help take some of the question marks off the table ( as well as leaving the door open for Chara to potential resign ) but i get the impression that they're prepared to let the kids get some time in as both Lauzon and Zboril have outgrown the AHL, even Clifton too. If things work out for them, half their starting D rotation will have come from their 2015 draft, which is pretty impressive. I don't know how many teams can say that.
And of course, there's always the possibility of this imploding, where all the new kids suck and McAvoy/Carlo/Grz get overwhelmed trying to hold things together. Time will tell.