It's mostly the rubberized grip that makes it feel so great. It's really pleasant to hold. Also, the control sticks are completely customizable in terms of resistance. That may sound like some gimmicky feature, but after you spend some time playing with it, you understand why it's such a big deal. I change the resistance from game to game. I like my left stick to be loose and my right stick to require effort when I'm playing shooters, and I like to tighten the left up when I'm playing racers.
In terms of the D-Pad, the individual nature of each direction is certainly an improvement over 360's giant fused wheel, but it's still not as good as a PS3's D-Pad. You won't be playing any fighting games with it if you like to exclusively use the D-Pad (but if you're a 360 user, you've already grown used to that). It works well for things like weapon selection and other secondary functions.
The face buttons, at least for me, are the real stars of the show. It immediately becomes apparent that Razer set out to make a controller that mimicked the feeling you get when you're playing on a PC. The face buttons feel like a click of the mouse (and sound like it, too). You're not left guessing if you hit the button properly. You get an immediate, audible response, and it happens so easily that if a game requires rapid presses, it's the easiest thing in the world to accomplish. Also, since the face buttons are proper switches instead of the typical 360 membrane system, the buttons won't accidentally depress the wrong way during a game, leaving you with a Y button that only works occasionally.
It also has two reprogrammable buttons near the top of the shoulders, if you're into that sort of thing. I've been using one of them to jump while aiming in Halo: Reach. It can add quite the tactical advantage.