I've been an iPhone user ever since the first iPhone and upgraded to every version of an iPhone, every other year I would upgrade at full price. What I can tell you is I've had the Atrix for only a few days and the customization that you can do with Android phones is Incredible.
I'll try and list what I like about it;
You can customize widgets to your home screen to display a mini version of your most used programs, I use it like a preview without having to open the program.
There is a bar across the top of the phone that has all the phone notifications.
I use the Finger print recognition to unlock the phone which I find it to be much faster than entering a code, there is a code backup just in case something happens to the fingerprint reader or if you are wearing gloves.
Downloading and Installing applications is faster than any phone I've ever used. There are a lot of Free apps on the Android Market that are paid apps on the App Store.
The best analogy I can tell you is; This phone is like a custom race car, It will take a few days to customize, but once you do, it's like nothing you've ever driven before.