Resizable and draggable windows lets you arrange items on the screen very similar to the way that you have items on a desk. It works - it isn't broken or out of date. When writing in a notebook on my physical desk, I do not want my notebook to be the size of my desk. I might be taking notes from a book. If my notebook was the size of the desk, how can I read my book? I can't.
Overlaying windows is brilliant. It isn't a problem to press Alt-Tab or use the taskbar. Personally, the grouped buttons on the taskbar is a nuisance as you need to click on it (XP) or hover over it and wait for a popup (7+) rather than just seeing loads of window buttons.
I have multiple hires screens but this doesn't suddenly mean I want one fullscreen window on each screen. That effectively reduces the windowing system to only displaying two items at a time. My physical desk has more - why should the computer suddenly be limited to only a couple of items?