I can understand people complaining. The dialog UI you linked to is a horrible grey text and grey, it's really hard to read. The rest seems to be a case of "flatten it, because it's modern", it really don't make thing more visible or clearer.
Again, this (insert three or four choice expletives) flat design meme that treats contrast as if it's an evil to be exorcised.
Never minding the fact that basic UI elements were moved for no good reason, the old UI differentiates the borders between elements a lot better than the new. Look at the layer selector in the first screenshot and compare it to the new one - the thicker lines between elements gives your eyes something to lock onto, and the elements "stand out" more. Colors are removed for.. why, again?
I know the advice is "engineers shouldn't design UIs", but I'm quickly coming to the conclusion graphic designers shouldn't either. Just about every UI convention of the last couple decades is being thrown out, or at least heavily modified, for something that's not necessarily better in any way.
Thank you!
Without having worked with the new UI, I do like the looks of the new palette. The form fields on the other hand look like they could be overseen easily.
There are also some screenshots and videos in the official blog post http://blogs.adobe.com/photoshop/2015/11/photoshop-cc-2015-a....