I mean, I'm not entirely opposed to some translucency and gloss if it doesn't get in the way of legibility. For me early Mac OS X 'Aqua' circa 2003 is the peak of that aesthetic.
Any UI theme should also be applied consistently. What I hated about Vista is the Aero theme was only surface deep. You were always only a few clicks away from some program that look liked it hadn't been updated since Windows 95.
Yeah, I've always hated that about Apple, and I primarily use Apple products. They have opened up a little bit in the last few years though. Like in macOS you can choose from a few different accent colors, you can turn borders on around buttons (I think that's a contrast setting in accessibility), you can turn off transparency, and you can change the color of your mouse cursor (mine is now hot pink—never lose sight of it).