It has a sturdy build with high-quality plastic, and the battery-cover is cleverly fitted into the phone-chassis.
The OS (currently updated Android v4.0.2 "ICS") differs quite a lot from v2.x (which I used before). All of the UI-interaction is now done completely via touch / multi-touch (which Google had envisioned when they started development on Android).
I especially love how you can drag-n-drop shortcuts on top of each other in the new launcher to form popup folders. One of several new, interesting and innovative UI functions. Another is the ability to take a screenshot of the device-display (pressing Power+Volume down buttons simultaneously).
I've been using Android full-time since the early v1.x-days, and personally I love the new UI guidelines, drop-down menus and generally, Android v4.x all-in-all :)
Google has done a magnificent good job in rolling v2.x (mobile-version) and v3.x (tablet-version) into one monolithic source-code tree, capable of making both binary-versions.
Keep up the good job guys! :D