I have one and I really like it, it's beautiful to use. I haven't used Android enough to compare it against, but having used an iPhone quite a bit, I think they're pretty even. iPhone is ahead on the the number and breadth of apps, but WP7 is better integrated (between contacts/facebook/pictures/twitter etc).

Regarding the voice commands, I've only ever used them to try them out (and results were patchy, maybe my South African accent), I couldn't imagine ever using them in everyday use, so I'm not too fussed about Siri (although it looks amazing from a tech point of view).