I don't get the hate
Windows 8.1 on a mobile is a perfectly lovely OS. As good as iOS, better than Android (battery life, basically, although I personally also prefer the interface). The only drawback, and it's a big one, is the shortage of decent apps for it.
I think its failure in the US market has been mostly about marketing. From what I hear, you just can't buy a Windows phone in huge swathes of America. Over here they're easy to come by, and they've got a respectable (double-digit) market share.