OS X changed substantially since Snow Leopard and paradigms were broken, you will have to adjust when you leapfrog like that. I have adjusted to these changes and actually feel disoriented now when I launch Snow Leopard. There are always two sides to a coin.
I happen to like fullscreen mode on my MacBook, even with Finder. It gives me more space, as Dock and menu bar are hidden, and I can swipe between them with gestures and Mission Control. I really like it that way. Truth be told, I don’t know why anyone would want to use fullscreen mode in a setup with a large screen or even multiple screens, but that is also just my opinion. Using separate Spaces makes a lot more sense, especially in combination with option + green button. I agree with aspic (above) that Apple should have at least offered a setting to change the default behaviour of the green button, but using option + green button or even just a double click on the window chrome has the exact same result. It’s a minor adjustment. I have used OS X since Leopard and there was to my knowledge no maximise button in the ordinary meaning of the word, it always adjusted the size to the window content.
Nevertheless, I sometimes use a second display as well and find that it works just fine for me (there were some problems with that in Lion). There is a downside to disabling ‘Displays have separate Spaces’ in System Preferences > Mission Control: it will interfere with Spaces and fullscreen mode and it is likely the cause of your problem with the YouTube videos. I really don’t recommend doing this if you’re using either of these features. On my system, the video also doesn’t vanish when I switch to another app, so that may be a bug on your system. The YouTube fullscreen video only closes when I close the corresponding Safari window or tab.
What is it that bothers you about seeing the menu bar on your other displays anyway, it’s not like the menu bar is a redundant design element; you will likely need it when you interact with applications on your other displays. Windows doesn’t have a menu bar like that, but it merges these menus into the application windows. The menu bar also becomes semi-transparent when no app is focussed on that display.
Some suggestions:
(1) There are Finder enhancements like TotalFinder or XtraFinder that address some of the issues you are experiencing with Finder, such as labels and coloured sidebar items. You should really have a look.
(2) There are tools that help you with the maximising, similar to the window-snapping feature on Windows 7 and later. Look in the App Store for Window Magnet, BetterSnapTool, Cinch, WindowTidy or others.
Edit: I’m confused now, this thread was recent when I opened it.
