I like the X series GUI paradigm and the improved window management. It's the size of the GUI elements that bother me. I recently opened Sonar 8.5, and thought, "oh wow, yeah, everything's the right size." Then I opened up X3 and it's like someone changed the zoom settings on my display.
Examples: look at the console strips in 8.5. Pay attention to width and vertical use of space, how many could you fit on your monitor? No look at X3 and do the same. 8.5 wins big time in the "most efficient use of screen real estate" category. On the subject of the Console view, the console strips are so big that you can't use it when it's in the multidock because you're constantly scrolling. This makes the multidock useless for me. Similar complaints with areas of the GUI like the toolbar. 8.5 and prior had a thin customizable toolbar that I could make as thin or narrow as I want. I kept them thin, and had everything I needed in a single toolbar row. This devoted a lot of space to the Track and Console views where I spend most of my time. Now look at the X series toolbar. It's huge. It takes up a ton of space. Same for the track inspector, much smaller in 8.5, but still had everything I need. In X3, it's much wider, really digging into the track view.
These kind of things end up being workflow killers for me, since I'm constantly closing docks to try and increase my screen real estate. Meanwhile, if X3 had a 75% zoom option, I'd probably love it. I really think Cakewalk is on the right track, but they really need to shrink down the GUI elements, at least for the non-touch screen users. Take a look at how a DAW like Studio One makse much better use of screen real estate. Or how Reaper's dynamically resizable console view makes using it while docked an absolute joy.
So...it's a mixed bag for me. Good idea, now shrink everything so I can see more stuff.