Ignoring the aesthetics, the usability (hence productivity) is... not good. Take zoom: ctl-mousewheeel. Fine, you might think, but that needs two hand and mousewheel zoom is much better. Indeed, that's what PCB does out of the box, but the schematic editor is the opposite. And there's no option to change it.
Then there's the right-click zoom. Where is the right-click unzoom to counter the very VERY tight zoom you just did because you went to pop up the context menu and accidentally gave the mouse a jiggle?
Oh, mouse buttons. Considering Windows mice don't usually come with middle mouse button (it's an awkward mousewheel press on mine), but let's say the price of an extra mouse just for this app is OK. In PCB you click and drag and it does more or less what you expect, but in schematic it pops up that little direction icon and you don't drag - you move in the direction you want to pan and the distance you move sets the speed. Except since it's based on Office code, seemingly, 'fast' is actually pretty slow. It is completely unintuitive for panning like that, particularly compared to to much better PCB.
All of the above could be mitigated by having mousewheel zoom without a modifier - you can easily zoom out/in to pan with one finger. Doesn't have to be the default either, just be able to set it somewhere.
Oh, and the damn thing pops up full screen every time it starts even though the launch link is set to normal. No high DPI support, 8 point text in the NIH menus, ...