I don't think it's the tile-based start menu that people have complaints with. At least for me, it's the notion that I should only be able to see one program at a time. (I've not actually played with Windows 8, so I may be wrong about that. If I'm wrong, let me know; I will try to play around with it, too.)

For one thing, I frequently reference one program while using another, and it seems to me that W8's GUI gets in the way of that.

Another thing is that I want my windows to be tall, not wide. Wide things are good at filling peripheral vision, but I don't use computers with my peripheral vision. It sounds like you know a lot about UI stuff, so I'll avoid repeating stuff about narrow columns, etc. Monitors are now wider than they used to be and MS wants for a program to take up the whole thing.

Ultimately, though, I don't really care, as I hope to never use Windows again.