The software is amazing. It's not tightly integrated as iOS but is definitely becoming better day by day.
It's new; its original and not just a ripoff. From apps to UI, it breaths originality and great seamless user experience. I have used HTC Mozart 7 which I got for my mom. Although the software is not straight forward, as my mom says, its still usable by at least a considerable amount of people who can easily use iOS.
The platform may have some 35k apps, but honestly, the apps are no where near to iOS. The quality and number is both lacking + Microsoft doesn't provide good APIs so that they apps may differentiate themselves. iOS has the best APIs on the planet for UI customisation and UI design which the others can only dream of. WP7/7.5 schema for design and implementation revolves around left/right scroll; so all apps are more or less the same - absolutely monotonous.
I have been using iPhone4S for 3 days and good lord, its the best thing I've ever used. I could never get the amount of apps and good apps on any other platform. Battery life's good as compared to HTC Mozart 7 even though it has a lot of location based stuff - runs on dual core processor with graphic intensive apps.
Summary - Anybody looking for a non-iOS/non-Apple platform - WP7,5 is the way to go.
Well done Microsoft. For once, I believe you have originality and conviction of making something better.
EDIT: As for the phone and the topic - the phone looks great but I can only wonder how uncomfortable would it be to actually use it given it has unyielding corners which may prove to be very uncomfortable in actual use.