Curiously, long before the phone's official announcement I had stumbled upon a plethora of comments claiming that the HD2 wouldn't have even halfway decent design due to its gigantic size. In my opinion, though, the HD2 is well-designed, benefiting from the combination of a thin casing, top-notch materials and a 4.3" screen. You won't be able to appreciate it, though, until you play around with the phone for a while.
Hardware controls found on the HD2 are few and far between - there is the volume rocker on the left-hand spine and five buttons sitting beneath the screen. It doesn't have a joystick or a trackball, furthermore, the power button is nowhere to be found, which is quite strange.
If I had to name one key feature of the HTC HD2, it'd definitely be its display. In spite of it having capped color palette at 65K colors and resolution of 800x480 pixels (which seems insufficient for a screen of this size), the HD2's display delivers.