Maybe it shouldn't irritate me, but it's the first time I've encountered it in 30 years. I'm all for change and trying new things, but this doesn't feel like progress.
And then ... Apple lost its way. Now when I get a new Mac I spend the better part of a day turning off as much of the pointless eye candy as I can so that I can focus on the task I'm working on, not the distracting UX conventions.
I want a computer, not an iPad with a keyboard. That already exists, and there is a reason I don't have one.