Windows Phone 7 snuck up on the world today, but having played with it, I'll tell you Microsoft is putting all it's muscle behind this. No matter who you root for, to be anything short of impressed is stupid.
How does it feel? Nothing like an iPhone, for starters. The slippery, rotate-y screens may take a little getting used to, but they feel right. Microsoft deliberately wanted to get away from icons and this notion that all behaviors get the same size button on the home screen, and you definitely get more of a sense of priorities here: Entertainment, social networking, photo sharing—those matter, and oh yeah, here's a phone if you need a call, and here's a browser if you need that too.
It's hard to tell from looking at this stuff, but much of it is customizable, including almost everything on that home screen. Don't let the uniformity of design language fool you, there will be a lot you can do to differentiate from other people....
I may have to invest in one because my ZuneHD runs off the same system that the Windows Phone will and my ZuneHD is amazing. Cool.