I switched from an Evo 4G to a HD7. It's interesting because they are almost the exact same hardware inside and out, but they could not feel more different in terms of user experience.
The first thing you'll notice is that it's REALLY FAST!! WP7 may only run on "old" Snapdragon processors, but it feels even faster than the latest dual-core Android devices. The speed affects everything:
- there is less input lag. I've found that using the on-screen keyboard is MUCH easier in WP7 than Android because it responds instantly every time.
- hitting the start button returns you to the home screen instantly, even if you were in the middle of something processor-intensive like watching a video or playing a 3D game
- scrolling & zooming webpages/photos is silky smooth
- navigating around the UI is super smooth and responsive, and never even shows a hint of lag or stutter, unlike every Android device I have tried
- it even boots up much faster!
- Going back to the home screen actually closes your app, reliably, every time!! (and saves the state if the app is designed to do so) Advanced Task Killer should NOT be an essential app for a freaking smartphone OS. No more wondering whether your app was actually closed or whether it's still running, slowing your phone to a crawl and draining your battery. No more wondering which app is the offender.
- The home screen manages to give you lots of information without appearing cluttered. It's a nice change coming from Android, with its multiple screens full of ugly-*** widgets, gaudy OEM-customized buttons and UI elements, icons, etc. Live tiles are brilliant in that there is no distinction between the icon and the widget.
- Even if you don't care about Xbox Live, the Live-enabled games tend to be very polished and full-featured. They are much higher quality than your typical smartphone games.
- I'd never used the Zune software until I got this phone, but I have to say, it's far better than iTunes as a way of managing and syncing your music collection. You can even sync your phone over your home wifi network.
Overall, WP7 is faster, more responsive, more fun to use, simpler, and more polished than Android.