Win8 is an infrastructure change for MS. Not all that many actual features. It's an attempt to make all phones, mobile devices, and PCs use the exact same OS (not a mobile variation of it like Windows CE -- the same OS).
Of note, however, is that to accomodate phones and the app installation, it means that Win8 can remotely track, install, and uninstall entire programs without your consent or your permission. Sure, they may say that's not what it's for NOW... but with that kind of big-brother loophole built in? I can't help but wonder how long it will take for them to start changing their EULA and their policies to let them do anything they want at the behest of the RIAA or the MPAA or the dept of Homeland Security.