I haven't used windows 8 that much, but i can say that Windows 8 came with improved internal functions (APIs), more security fixes (and annoyances), new interface (and adds), and it just uses about the same amount of memory than windows 7.
In the other hand and what bothers me more on every windows version change is the compatibility for older programs,when i saw my own game stoped working and i was like: "wtf with windows 8", and when i saw what i needed to do to make it to work again i got mad.
My expensive engineering programs needs to be repurchased, or upgraded ($$$) just to work on that.
I hardly get used to the new interface because i get troubles to find what i want, but its just matters of time to get used to it.
The file explorer really STINKS A LOT compared to windows XP, since windows vista they are going backwards on each windows version on the file explorer.
Sorry but I stay on my old windows version until i see its worth to change
conclusion:
For common users windows 8 will be great, but for engineers, and computer nerds: "omg windows you stink more each day".