HEADLINE: Sort out the default colour scheme
I can't really comment on the more technical side, but the Ubuntu Grey/Purple/Orange colour palette is horrible - it makes the whole desktop feel claustrophobic. There's something icky about it.
Together with the 'quirky' Ubuntu font, which is hard to read at small sizes and not at all helped by Linux's mediocre font rendering, it makes for a fairly unpleasant experience.
Your designers should be looking at Elementary OS for how a pleasurable desktop could be designed, even if it's a bit to close to Mavericks-era macOS.
(I know it's possible to change the theme, but none of them have the fit and finish that a first-party one would have)
ROLE: Graphic and UX designer (who wants to love Ubuntu but can't for superficially visual reasons)