The screen is beautiful, I love just unlocking my phone to stare at it.
I LOVE the camera button. I use my camera quite a bit and on my old Android I had to power on the screen to get to the camera. Now I just have to press a button!
The OS looks great, it's super smooth, and I love how it's integrated into most parts of the phone. The hubs, the store, the apps all look great!
Speaking of integration, the social network integration is amazing. I was able to easily link all of my SIM contacts to their facebook and twitter accounts and the people hub brings it all together so nicely.
And there's a lot more I love about this phone and WP8