I used the free Beta version when it was offered before the current version was released. Honestly I was quite disappointed. The product is obviously targeting the mobile market. Once you get past the start screen I really didn't see that much difference.
I removed the Beta version only after a few days of use because I really didn't see any improvements that I was really interested in.
Yes there are some security advances however most of them have been available in Linux for years.
I think if Microsoft really wants to go after the mobile market they should offer an operating system specifically designed for that purpose rather than trying to make a hybrid desktop / mobile operating system.
Trying to be everything to everyone just makes it too big, too slow and inefficient.
I for one use my desktop computer and my mobile devices for completely different things and I want an operating system(s) that helps me use those devices to their maximum efficiency.