Aqua is still a revelation. We've taken a huge step back in being able to just identify window controls. My hope is that some of that comes back with Liquid Glass, but honestly, Aqua still looks great.
What all the copy cats missed (Windows Vista, Linux themes) is how consistent and usable everything was. It looked great, but better than that, it worked great.
I loved the "stripy" windows. Things lining up perfectly on the horizontal stripes were somehow so visually pleasing.
I tried to replicate this look in my Java Swing UI using a commercial Aqua-like look&feel, but got hit by issues with controls rendering their own background, resulting in stripes being misaligned.
I was so disappointed when Apple phased it out later.
What all the copy cats missed (Windows Vista, Linux themes) is how consistent and usable everything was. It looked great, but better than that, it worked great.