As a product it clearly failed. It did not meet its sales numbers at all, they had to extend XP's life over and over and finally killed the gift horse so that Vista would be installed on machines by default. Many people would choose XP over Vista if they could on their machines. I think most people would reasonably call it a failure from a business perspective.
Vista failed? That's news to me. Care to elaborate on your definition of success?
I've been using it since it came out and like it just fine.
I can understand saying Vista had problems, or bugs, or that it had a lot of PR issues, or even that some vendors didn't like or want it. But fail?
I think maybe you've been listening inside the web echo chamber a little too long.