I don't consider Vista a failure. ME was pretty much a fail, though.
I don't like Vista because it was designed from the bottom up to be friendly to stupid users and it made doing certain things much more difficult for power users who had been using XP for so long. Also, it gave a false illusion of security to the aforementioned stupid users by asking for permission for every little thing...
If anything, Vista seems like a beta for Win 7...