I previously thought it was growing pains and they would eventually land on a great style that was still "theirs", but at this point it feels like a lost cause. Personally I've stopped recommending Ubuntu on the desktop because I already know what the initial reaction to a fresh install is going to be.
I could sit and tweak a Linux install for hours, kind of like an old car. But of course I never get any work done that way.
And the lack of a flat UI does not count as an argument - that's just a fashion trend.
Also, my own anecdotal experience does not match yours. I often get surprised (as in "wow, that looks nice!") questions of "That's not Windows/OSX? What is that?" from people when I show something on my laptop.
But be that as it may, I doubt this is what causes the downvoting. I'm pretty sure a statement like "colors and icons are ugly" would have provoked a similar reaction.
Stating something like "X is inconsistent with Y making the whole thing restless and messy, and if they did the font alignment like this the whole thing would have a more orderly clean look" wouldn't have.
Saying "X is ugly" is not much use and is mean, thus more likely to attract downvotes.
Saying "I think X is ugly. Here's why {list of subjective reasoning}" may be useful and is not as mean.
(Note that I'm not saying Nathan Osullivan is necessarily wrong in his judgement - I might disagree with it but he can still have valid reasons for disliking it. It's just that it's pretty a useless remark if he gives no arguments why he has that opinion)
Negative energy is quite unproductive.
Then there are the multi-colored icon boxes (why do the icons need boxes around them at all?) that all clash with each other and clash with the (ugly) purplish theme, and clashes against the gradient black top toolbar (which has virtually no padding by the way).
It doesn't take a great designer to notice these things, god knows I'm not one. But I've worked with designers at every company I've worked for, small or big, and all of them would have done a (much) better job than Unity. Which tells me either no designers were involved or they were outvoted at every decision.
The default Ubuntu font is just not consistent and readable enough for a UI. They need to find something like Segoe UI, that gets out of the way and is easy to read.
I really do agree with the gp and your opinions regarding the design. It is important, and I do think Ubuntu should get some outside opinions for the next LTS and revamp their design based on some of the fundamental practices.
I do enjoy tweaking the fonts until it pleases my eyes most. I've been using Source Code Pro as the monospace font for quite a while now. Currently trying out Alegreya Sans and its variants for the regular system font - kind of controversial among my designer friends: some of them consider it too "serify".