Competitively, the new detachment isn't good. It's not garbage since it does give decent choices and only the elite section is trash, but the other two tax units can be Havocs, which can get Autocannons and can do good, and Bikes, which are awesome. Obj Sec on those Bikes and Havocs mean you have a good pair of units to take and hold Objectives. Downside is that Plague Marines lost theirs, which is a blow. And giving Raptors and Warp Talons the charge when they come in, that's amazing.
From a fluffy perspective, and I keep my CSM fluffy, I couldn't be happier. The detachment is very nearly my army, with the exception of Havocs which I need to pick up. I may end up taking a CAD regardless for the miscellaneous stuff I like to bring, but the core Detachment looks useful, and some of these Auxillaries are good enough to see the table at 2k and maybe even 1850. I haven't run the numbers yet. It doesn't fix the codex, but it does fix how they can be run casually. I'm still not bringing them against my local tournament meta, but that's okay.