As mentioned elsewhere, the Stackable FX is a real boon, as is the Control Bar.
Being able to collapse all the Modules I don't use that often, but being able to mouse over to view the controls is quite a neat idea. Maybe better than my previous suggestion of having the Control Bar horizontally scrollable.
And the Custom Module is an absolute joy. I've been messing about this afternoon with a few mixes while updating my keyboard shortcuts and colours etc, and realising just how much I've missed a few of the buttons from 8.5.
Although through X1,2 and 3 I've 'improvised' using keyboard shortcuts (even going to trouble of setting up a lot of my most used functions to require only a single key stroke), just having a few of my most used features a single click away is back like it used to be. Here's how it's looking at the moment:
It would be nice to have more buttons, or the ability to load more than one Custom Module onto the Bar, but what we have for the time being is pretty cool.
Mix Recall is a great idea - it's completely intuitive and easy to use, and if you want to get really sophisticated in how it works, there are a raft of options that can be set to be remembered and recalled:
Last but not least, I'm pleasantly surprised by how good the ReMatrix Solo convolution reverb Pro-Channel Module is. Some well thought out presets and a fair few adjustable parameters:
Incidentally, does anyone know if the Rematrix is also supplied as a VST with Platinum? I've done a fresh scan but it doesn't appear in the Plug-in Manager, so I'm guessing not.