On "regular computers" I think it was flawed in two fatal ways:
- there was already an extremely heavy expectation that clicking the start button or pressing the windows key would bring up a menu, not a full screen takeover where all contextual sense of place (that you had in the past experience) was lost.
- the UI being a full-screen takeover on a phone (Windows Phone) or a tablet (10"-ish tops at the time) was OK but on a 21~27" desktop it's absurdly overwhelming.
If you had good Live Tiles there was a ton of information density. You could have the weather, your calendar, recent emails, recent tweets, recent photos, interesting news, etc all on one at-a-glance screen (versus the phone form factor where you'd need at least some scrolling).
It felt like wasted space on the desktop because it was originally hard for desktop apps to opt-in to Live Tiles and send Live Tile updates and not enough people were using the sorts of multi-platform apps that had great Live Tiles.
Sadly grids of unrelated data aren't good for information at a glance. A wall of post-it notes will never beat a structured list; the old Start menu was a structured list, where you knew things were always in the same place (the Programs submenu didn't move or say "software" sometimes, and "programs" other times) whereas the Windows 8 menu was a wall of random post-it notes flung on the screen and you're meant to gaze over the entire thing to look at unrelated data and somehow make sense of it.
A wall of post-it notes can be incredibly handy to the person that placed the post-it notes. The Start screen was never "random", it was designed for customization and personalization. Programs stayed where you told them to in the groups and sizes you wanted them to. Choosing a size would affect how much data an app could show. The program might provide a tile of new data it would show some of the time, but the program's name and icon would still show up in most of the tile variants (and hover tooltips worked on Desktop), and any app could only have at most 3 tiles at a time. The timing of tile flips was a bit random, but there was also a general rhythm to it you would pick up if you used it a lot. It was a very intentional "dance".
At least in my experience there was a lot of sense to it. I had a lot of data organized to my liking in Windows 8.
The start screen is something you just had to get used to. I think it's more comfortable than the menu. Effectively it works as a second desktop to put application shortcuts on. I have about 30-40 on mine (on Windows 10, mind you), which is way more than would fit on a menu without submenus.
Especially with such a low information density. It was clearly just a massive amount of wasted screen space on desktop.