And I'm sure some people greatly like (or will come to greatly like) Liquid Glass. Personally, I think I like the overall concept better than the flat UI, but there's no question that in comparison, Liquid Glass is very unpolished. My biggest problem with flat UI was that everything was ... flat. I think that's part of what's been driving me back to late 90's UI themes too. We have fancy, complex machines capable of faking 3d perspectives in amazing ways and for way less compute cost than we paid for it in the late 90s. And depth can convey a lot of information that you can easily lose in a flat UI.
But there are some real rough edges to be sanded down still. There are places where the transparency effects mean the underlying color/text bleeds into the menu / UI text that you actually want to read. It happens way less than you'd expect from critical screen shots, and a lot of the time it's less that it makes the UI text unreadable and more that it makes it look like a graphical glitch. But it does happen, that's not great and needs to get cleaned up.
There's also a weird level of "flatness" to some parts of the UI, that seem to rely on color contrasts to get the depth, but then that means that in certain situations the depth that should be there is missing. A good example if this is the safari button bar. On a site like HN where the background is white/off-white, the buttons and their bezels just sort of look like a flat white on a flat light grey. A site with a solid dark grey like daringfireball's website on the other hand allows the edges of the buttons to give a little bit of depth, but there's basically 0 contrast between the control backgrounds and the bar background. But then a site like slashdot has a medium grey background and now the buttons not only have color contrast but the slight shading around the bottom edges gives them depth that's not present in either of the other cases. When it works, the effect is nice, the problem is their theming system isn't (yet?) smart enough to make it work all the time.
I don't have problems with flat. I do have problems with unnecessary borders around buttons. In my opinion, space separates design elements enough and borders, beautiful as they are, with glass transparency effects and other bells and whistles, is just a visual clutter. And Liquid Glass design introduces quite a lot of new borders upon borders upon borders, in a style quite resembling an unholy love child of Windows Vista and flash websites of the 00s.
The could definitely do with cutting down some of the empty space and the “border stacking” problem that feels like old fashioned “div padding” stacking when doing html, though I feel like that trend started a few versions back in the flat ui design. Interestingly the iPhone version of Liquid Glass seems to have much less “extra” white space than the Mac version of it, which seems backwards because the iPhone should need/want more for larger touch targets. Or maybe it’s just less noticeable because it needs those large touch targets but also lives on a smaller screen.
I guess it's part of the trend now. Some time ago both Google and Apple rolled out very flat UIs -- Apple in iOS 7 and Google with Material Design in Android 5, and both where mostly flat. I don't know, maybe they were influenced by Microsoft's Flat UI that ultimately went nowhere. Yet, over time, Google began introducing more and more meaty designs with more aggressive rounded corners, eventually ending up doing everything very curvy. Maybe folks at Apple looked at that and wanted some of those curves, too. So previously the trend was to flatten everything, now the trend is the reverse of the previous.
