I think the best move for MS on this would have been to make Metro optional and perhaps add a couple of other features.
I love using metro, but not everybody does and in that regard I think it's a shame. Regardless, you can still get rid of it, so anybody who gets a computer with Win 8 on it doesn't have to be forced into using metro.
I don't think it's THAT much of a failure, needs some changes/improvements. I just think it fails to win over many metro sceptics and people who dislike metro and I think it could have been marketed better.
For touch devices as well, the metro interface is fantastic, I've preferred it over all other touch-friendly interfaces, whilst I do not use the touch features on my Win 8 PC, I love it on my Windows Phone 7.8, it was actually one of the deciding factors in purchasing the phone. Having said this, I have been thinking of buying a monitor (I use a HDTV at the moment) and I've seen touch screen IPS monitors like
this one: I might find it tempting to get one, not just to utilise a touch interface but also as a graphics tablet, might be useful for texturing 3D models (for example) and drawing various concepts - I suck artistically with a mouse, so it works an alternative to something like a Wacom, as I was previously thinking of buying one.
With thinks like touch monitors I can see why MS decided to use the metro interface with their desktop OS. And whilst I am a lover, I will admit there are things MS should have done better, but of course those things don't really affect me as such.