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...
Ha
I though the same thing about windows xp when I moved to that.
Before I started using xp I'd been working as a sys admin using nt4, and windows 2000, (desktop and server editions).
When xp first came out it was referred to as duplo windows named after the pre-school logos that are huge so that they can't be a chocking hazard.
Given time you just learn to adapt is all.
I don't think that vista is/was a failure. It didn't have good uptake because xp was still running just fine and was fully supported by ms, so business didn't get it, it missed half the features that it had promised, so geeks didn't get it (or fewer got it), in lots of cases it required new hardware, which was a bit of a shock for some,
Previously it'd been possible to upgrade windows 95 machines to windows 98 with no hardware changes, if you were really lucky with your original 95 machine then you might even have been able to install xp too, it didn't require a brand new machine (266 with 64mb ram when it first came out!)
So you're average not too computer literate (the kind who don't even install service packs) didn't get it.
And finally, ms told everyone that they were working on it's replacement before it was even finished!
Vista just feels like a beta for windows 7. Like it'd been 8 years since they'd released a new os and they had to release something.
I wouldn't say that it failed though. I don't really think it was ever meant to succeed, just like how telling everyone that me was the last of the dos releases and 2000 was the future pretty much secured the fate of me (though that is was rubbish.)