Better described as a service pack with a new paint job. Windows 7 is built from Vista. The biggest changes are the default settings they are choosing over what they did with Vista. But if you really want to, you can make it exactly like Vista, without a whole lot of effort.
It will be less buggy that Vista, by virtue of including all the bug fixes from Vista, and by disabling many things that caused a lot of grief in Vista.
Yes, I have already delved into Windows 7. Took me 1.5 hours to turn it back into Vista. Still has the same exact memory and thread manger as Vista, including the bugs.
It should be free to anyone who bought Vista. To charge any more than that would be criminal, in my opinion.