Ask some people why Windows Vista failed and they will tell you that most of the problem came from hardware compatibility. I don’t remember ever having problems with Vista back when I used it. Then again I was running it on a brand new computer with the OS in question preinstalled.
And that’s another thing, I think you’re pretty much expected to upgrade your hardware at least every few years. I’d like to think that the people who had problems with Vista kept the same white-box PC they’ve had since 98SE, or even 95. Vista ran great if you had the right hardware. Maybe if Microsoft had optimized their OS even for XP-era machines it would have seen greater adoption.
I also really liked the Aero glass theme, it made younger me feel like I was in the future. Those gadgets at the side of the desktop were pretty cool too. Overall I think it was definitely ahead of its time, and with support for current software and hardware, would have been a solid choice for average computer users today.
They tried to change too much at once. The change between 98,ME,98SE, and XP UI were gradual improvements. Then Vista came along and did almost an overhaul of the UI. They refined the UI for 7 which people liked.