It's basically Windows 7 but a bit quicker, with a new start menu and a few new features (useful ones, too). Unless the few new features seem interesting though, it probably isn't worth the upgrade. That being said, I've been using the release preview and things are going great, and while I haven't gotten around to mounting any ISOs or testing how cloud settings or USB booting works I'll definitely be glad they're there when I need them.
Also, for anyone reading this that still hasn't worked it out - WINDOWS 8 ISN'T RESTRICTIVE OR CLOSED DOWN IN ANY WAY THAT PREVIOUS VERSIONS WEREN'T. The settings, functionality, and desktop are still there, for the desktop/laptop releases the Metro interface is just a start menu replacement that can also have gadgets on it (though I can't speak for the version for ARM processors in tablets which may be more like a mobile OS).
Also, for anyone reading this that still hasn't worked it out - WINDOWS 8 ISN'T RESTRICTIVE OR CLOSED DOWN IN ANY WAY THAT PREVIOUS VERSIONS WEREN'T. The settings, functionality, and desktop are still there, for the desktop/laptop releases the Metro interface is just a start menu replacement that can also have gadgets on it (though I can't speak for the version for ARM processors in tablets which may be more like a mobile OS).